Reversible variable drives and systems and methods for control in forward and reverse directions

ABSTRACT

A ball-planetary continuously variable transmission (CVT) capable of stable control in forward and reverse rotation over a range of speed ratios including underdrive and overdrive is provided. Imparting a skew angle (zeta) causes unbalanced forces that change the tilt angle (gamma), resulting in a change in speed ratio of the CVT. Angularly orientating a control system of the CVT with a positive offset angle (psi) configures the CVT for operation in a first direction of rotation or angularly orientating the control system with a negative offset angle (psi) configures the CVT for operation in a reverse direction of rotation. A control system for configuring the offset angle (psi) may lead or trail the planets. The control system may configure a larger offset angle for more stable control or may configure a smaller offset angle for higher sensitivity in potential rollback scenarios.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/810,832, filed Feb. 26, 2019, which is hereby incorporated byreference in its entirety.

BACKGROUND

To assist with the description of embodiments, the following descriptionof the relationship between tilt and skew is provided, in which FIGS.1A-1C depict coordinate systems in reference to embodiments of certaincomponents of a ball-planetary continuously variable transmission (CVT).

As depicted in FIGS. 1A-1G, CVT 100 includes planets 108 in contact withsun 110 and traction rings 102, 104. Planets 108 are interposed betweenand in contact with first traction ring 102 and second traction ring 104at, respectively, first angular position 112 and second angular position114. FIG. 1A depicts global coordinate system 150 (defined herein toinclude axes x_(g), y_(g), z_(g)) and planet-centered coordinate system160 (defined herein to include axes x, y, z). Global coordinate system150 is oriented with respect to longitudinal axis 15 of CVT 100, withthe z_(g)-axis coinciding with longitudinal axis 15 about which planets108 are arranged. Planet-centered coordinate system 160 has its originat the geometric center of each planet 108, with the y-axisperpendicular to longitudinal axis 15, and the z-axis parallel tolongitudinal axis 15. Each of planets 108 has axle 103 defining a planetaxis of rotation (defined herein as planet axis 106). Planet axis 106may be angularly oriented in the y-z plane relative to the x-axis attilt angle (gamma) 118. Tilt angle (gamma) 118 determines the kinematicratio between the rotational speeds of traction rings 102 and 104. Eachplanet 108 has a rotational velocity w (omega) about planet axis 106,depicted in FIG. 1A as planet rotational velocity 122. Planet axis 106is defined by planet axle 103. In planet-centered coordinate system 160,the x-axis is directed into the plane of the page (though not shownprecisely as such in FIG. 1A), and the z-axis is parallel tolongitudinal axis 15. For purposes of illustration, tilt angle (gamma)118 is generally defined in the y-z plane.

As depicted in FIGS. 1B and 1C, planet-centered coordinate system 160 isresolved further to illustrate the angular adjustments of each planetaxis 106 used in embodiments of skew control systems. As depicted inFIG. 1B, tilt angle (gamma) 118 can be derived by rotating coordinatesystem 160 (with planet axis 106 in the y-z plane) about the x-axis toachieve first relative coordinate system 170 (x′, y′, z′). In relativecoordinate system 170, planet axis 106 coincides with the z′-axis. Asdepicted in FIG. 1C, skew angle (zeta) 120 can be derived by rotatingcoordinate system 170 about the y-axis (not the y′-axis) to achievesecond relative coordinate system 180 (x″, y″, z″). In relativecoordinate system 180, planet axis 106 coincides with the z″-axis. Skewangle (zeta) 120 is the angular orientation relative to the y-axis inthe x-z plane of the planet axis 106. In some embodiments, tilt angle(gamma) 118 is controlled, at least in part, through an adjustment ofskew angle (zeta) 120.

As depicted in FIG. 1D, certain kinematic relationships betweencontacting components of CVT 100 explain how the inducement of a skewcondition generates forces that tend to adjust tilt angle (gamma) 118.As used herein, the phrase “skew condition” refers to an orientation ofplanet axes 106 such that a non-zero skew angle (zeta) 120 relative tothe y-axis exists. Hence, reference to “inducement of a skew condition”implies an inducement of planet axes 106 to align at non-zero skew angle(zeta) 120. In certain embodiments of CVT 100, certain spin-inducedforces also act on planet 108. In CVT 100, traction rings 102, 104 andsun 110 contact planet 108 at three locations to form traction orfriction contact areas. In certain embodiments, first traction ring 102drives planet 108 at contact 1, and planet 108 transmits power to secondtraction ring 104 at contact 2. Traction sun 110 contacts tractionplanet 108 at contact 3, which may be a single point (shown) or maycollectively refer to multiple contact points (not shown here forsimplicity). Contact points 1, 2 and 3 are arranged in FIG. 1D toreflect a view of the x-z plane as seen from above CVT 100. However, forease of understanding, since contact areas 1, 2 and 3 are not coplanar,contact-centered coordinate systems are used in FIG. 1D so that contactareas 1, 2 and 3 can be illustrated with the x-z plane. Subscripts 1, 2,and 3 are used to denote the specific contact area for contact-centeredcoordinate systems. The z₁, z₂, and z₃ axes intersect at the center of aspherical traction planet 108.

As depicted in FIG. 1D, the surface velocity of first traction ring 102is denoted in the negative x₁ direction by vector V_(r1) and the surfacevelocity of planet 108 is represented by a vector V_(p1); the angleformed between the vectors V_(r1) and V_(p1) is approximately skew angle120. The resulting relative surface velocity between first traction ring102 and traction planet 108 is represented by a vector V_(r1/p). Atcontact area 3 between traction planet 108 and traction sun 110, thesurface velocity of traction sun 110 is represented by vector V_(sv) andthe surface velocity of traction planet 108 is represented by vectorV_(ps); the angle formed between V_(sv) and V_(ps) is approximately skewangle 120. The relative surface velocity between traction planet 108 andtraction sun 110 is represented by vector V_(sv/p). Similarly, forcontact 2, the surface velocity of traction planet 108 at contact area 2is represented by vector V_(p2) and the surface velocity of secondtraction ring 104 is represented by vector V_(r2); the angle formedbetween V_(p2) and V_(r2) is approximately skew angle 120; the relativesurface velocity between traction planet 108 and second traction ring104 is represented by vector V_(r2/p).

The kinematic relationships discussed above tend to generate forces atthe contacting components. FIG. 1E depicts a generalized, representativetraction curve that can be applied at each of contact areas 1, 2, 3,illustrating a relationship between the traction coefficient μ and therelative velocity between contacting components. The tractioncoefficient μ is indicative of the capacity of the fluid to transmit aforce. The relative velocity, such as V_(r1/p), can be a function ofskew angle 120. The traction coefficient μ is the vector sum of thetraction coefficient in the x-direction (μ_(x)) and the tractioncoefficient in the y-direction (μ_(y)) at contact area 1, 2, or 3. As ageneral matter, traction coefficient μ is a function of the tractionfluid properties, the normal force at the contact area, and the velocityof the traction fluid in the contact area, among many other things. Fora given traction fluid, the traction coefficient μ increases withincreasing relative velocities of components, until the tractioncoefficient μ reaches a maximum capacity after which the tractioncoefficient μ decreases with increasing relative velocities ofcomponents. Consequently, in the presence of skew angle 120 (i.e., undera non-zero skew condition), forces are generated at contact areas 1, 2,3 around the traction planet 108 due to kinematic conditions.

Based on the traction curve depicted in FIG. 1E and the diagramsdepicted in FIGS. 1D and 1F, V_(r1/p) generates a traction forceparallel to V_(r1/p) with a component side force F_(s1). Increasing skewangle 120 increases V_(r1/p) and, thereby increases force F_(s1)(according to the general relationship illustrated in FIG. 1D). V_(sv/p)generates force F_(ss), and similarly, V_(r2/p) generates force F_(s2).Forces F_(s1), F_(ss), and F_(s2) combine to create a net moment abouttraction planet 108 in the y-z plane. More specifically, the summationof moments about traction planet 108 is M=R*(F_(s1)+F_(s2)+F_(ss)),where R is the radius of traction planet 108, and forces F_(s1), F_(s2),and F_(ss) are the resultant components of the contact forces in the y-zplane. The contact forces, also referred to here as skew-induced forces,in the above equation are as follows: F_(s1)=μ_(y1)1N1, F_(s2)=μ_(y2)N2and F_(ss)=μ_(ys)N3, where N1, N2 and N3 are the normal forces at therespective contact areas 1, 2 and 3. Since the traction coefficient μ isa function of relative velocity between contacting components, thetraction coefficients μ_(y1), μ_(y2), and μ_(ys) are consequently afunction of skew angle 120 as related by the kinematic relationship. Inthe embodiment illustrated here, a moment is an acceleration of inertiaand the moment will generate a tilt angle acceleration {umlaut over(γ)}. Therefore, the rate of change of tilt angle {dot over (γ)} is afunction of skew angle 120.

FIG. 1G depicts a top view of one embodiment of traction planet 108having non-zero skew angle (zeta) 120, which results in planet axis ofrotation 106 being non-parallel (in the y_(g)-z_(g) plane) tolongitudinal axis 15 of CVT 100 and rotational velocity 122 of tractionplanet 108 is not coaxial with the z-axis. Skew angle 120 generatesforces for motivating a change in tilt angle 118. In the presence ofskew angle 120, traction planet 108 would have rotational velocity 122about an axis z″, and tilt angle 118 would be formed between axis z″ andthe y-z plane.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

Embodiments of CVTs disclosed herein are capable of operating accordingto the above-mentioned principles during operation in forward directionand reverse direction, may switch between operation in forward directionand reverse direction, and may be controlled using various controlschemes that enable switching between operation in forward direction andreverse direction. In particular, embodiments disclosed herein include avehicle or equipment with a transmission, drivetrain, CVT or a controlsystem for a CVT having a control system coupled to a plurality oftrunnions coupled to each axle in a plurality of axles, wherein thecontrol system is capable of misaligning the axles to adjust a speedratio over a range of speed ratios between underdrive and overdrive (andincluding 1:1), and configurable to operate in forward and reversedirections and further configurable to operate according to differentcontrol strategies for stability and sensitivity.

Advantageously, embodiments disclosed herein may operate in eitherforward direction or reverse direction, allowing a CVT to becontinuously adjusted to maintain a constant output speed for varyinginput speeds and torques, to maintain a speed ratio for variable inputspeeds and torques or variable output speeds and torques, or to providevariable output speeds for constant input speeds and torques.Furthermore, when radial translation of trunnion extensions results intrunnions oriented with an offset angle (psi) that reverses signs (thatis, switching from positive to negative or negative to positive),embodiments may proactively, simultaneously or reactively adjust a speedratio of a CVT. As such, if a CVT is operating in overdrive in forwardand trunnion extensions are radially translated to reorient thetrunnions to reverse the sign of offset angle (psi), the CVT may also beadjusted from overdrive to underdrive. Furthermore, control of a CVTbetween operation in forward direction and reverse direction may includeradially translating trunnion extensions to change the orientation oftrunnions relative to a pitch circle to accommodate a switch in thedirection of rotation and compensating for the corresponding switchbetween overdrive and underdrive by axially translating trunnionextensions to apply a skew condition to maintain the skew angle (zeta)imparted on the planets. The processes of orienting the trunnions to anoffset angle (psi) relative to the pitch circle to configure the CVT forswitching between operation in forward direction and reverse directionand applying a skew angle (zeta) to adjust a tilt angle (gamma) of theCVT adjust the speed ratio of the CVT to any speed ratio betweenunderdrive and overdrive may be performed independently, allowing formultiple possible control schemes for a CVT, such as an example CVT 200described below.

To configure a CVT for operation in a forward direction or a reversedirection, embodiments may translate trunnion extensions radially inwardor outward of a pitch circle to orient trunnions to have a positive ornegative offset angle (psi). Furthermore, embodiments disclosed hereinmay adjust tilt angles (gamma), angular positioning (beta), skew angles(zeta) and offset angles (psi) independently or concurrently, allowing acontrol system to switch operation of CVT between forward and reverserotation, and adjust or maintain a speed ratio.

Couplings between trunnions and trunnion extensions allow trunnionextensions to move axially but allow trunnions to rotate to a targetoffset angle (psi) about their respective z-axes.

Embodiments disclosed herein may advantageously orient trunnions at anoffset angle (psi) and adjust a tilt angle (gamma) of axles for a CVTconcurrently or independently, allowing for controlled operations inboth forward and reverse directions, wherein an offset angle (psi) signcan change at any ratio range, and a transmission ratio (speed ortorque) may be adjusted at any offset angle (psi). Advantageously, if acontrol system for a vehicle operating a CVT determines that a rollbackscenario is occurring or likely to occur, a control system may initiateradial movement of couplings or trunnion extensions or change anorientation of trunnions to change the offset angle (psi) sign relativeto the pitch circle. Instead of disconnecting power to avoid rollbackdamage or locking the CVT at a set angle to mitigate rollback damage,changing the offset angle (psi) independently or concurrently withchanging the tilt angle (gamma) allows the control system (and thereforethe operator) to maintain positive control of the CVT even in rollbackscenarios.

Embodiments of a control system may also determine a controlsensitivity. The control sensitivity is a function of the offset angle(psi) and dimensions of components including links. Small offset angles(psi) or short link lengths require less axial movement to achieve thesame tilt angle (gamma) and allow for faster ratio adjustments but maybe less stable. Larger offset angles (psi) or longer link lengthsrequire more axial movement to achieve the same tilt angle (gamma) andmay limit ratio adjustment rates but may be more stable. Embodiments ofa control system may determine a control sensitivity based on operatorinput, sensor information, or some combination. Embodiments may alsooperate according to a first control sensitivity under a first set ofconditions and change to a second control sensitivity under a second setof conditions. In some embodiments, a first set of conditions maycorrespond to operating a CVT in a forward direction and a second set ofconditions may correspond to operating the CVT in a reverse direction,operating in a forward direction when reversal of rotation direction isimminent, operating in a forward direction when reversal of rotationdirection is probable, in a forward direction when reversal of rotationdirection is possible, operating in a forward direction under anincreased load, or operating in a forward direction at higher vehiclespeed. Other conditions may be based on sensor inputs. In someembodiments, if a sensor determines battery capacity is low orcomponents are overheating, a control system may determine a controlsensitivity that limits the axial movement of a coupling and reduce theoffset angle (psi) to allow for reduced axial movement of the couplingor may increase the offset angle (psi) and reduce the frequency ofcommands for adjusting the axial movement of the coupling.

In a broad respect, embodiments disclosed herein may be generallydirected to a ball planetary continuously variable transmission (CVT)comprising a plurality of spherical planets between and in contact withtwo traction rings and a sun, each planet having an axle and a geometriccenter through which an x-axis, y-axis and z-axis intersect, wherein theplurality of geometric centers define a pitch circle for the pluralityof planets, wherein each axle extends through a central bore of aspherical planet and defines the z-axis and an axis of rotation. In somesuch embodiments, each planet axle is capable of tilting in a first skewplane, and has a skew angle defined as an angle between the central axisand the planet axle, and in a second tilting plane defining a tilt angleas the angle between the central axis and the planet axle, wherein thetilt angle defines a transmission ratio of the transmission. Someembodiments have a first carrier half coaxial with and rotatable aboutthe central axis, the first carrier half coupled by a plurality of linksto a first end of each of the planet axles; and a second carrier halfcoaxial with and rotatable about the central axis, the second carrierhalf coupled by a plurality of links to a second end of each of theplanet axles. In some such embodiments, the first carrier half andsecond carrier half are rotatable with respect to each other to definean angular position, wherein relative rotation of the first and secondcarrier halves defines a non-zero angular position that imparts anon-zero skew angle, and wherein a non-zero skew angle imparts anadjustment to the tilt angle, resulting in a change in the transmissionratio of the CVT. In some embodiments, a plurality of couplings couplethe plurality of links to the first and second carrier halves, whereinthe plurality of couplings are adapted to allow the plurality of linksto rotate out of plane with the first and second carrier halves tofacilitate the tilting of the planet axles. The plurality of couplingsmay be ball joints. The plurality of links may be flexible. In someembodiments, the CVT further includes a pitch circle coaxial about thecentral axis and having a radius equal to a plurality of centers of theplanet assemblies, a plurality of connections that connect the pluralityof links to the plurality of planet axles. An effective offset angle isdefined by the tangent of the pitch circle at a respective one of theplurality of connections and a line between an associated one of theplurality of connections and an associated one of the plurality ofcouplings. In such embodiments, the effective offset angle may bepositive when the plurality of links are located radially outside of thepitch circle, a positive offset angle associated with a forwarddirection of rotation, and the effective offset angle may be negativewhen the plurality of links are located radially inside of the pitchcircle, a negative offset angle associated with a reverse direction ofrotation. In certain embodiments, the CVT further includes an actuatoradapted to adjust the radial position of the plurality of couplings inorder to adjust the effective offset angle. Certain of these embodimentsinclude an actuator adapted to adjust the radial position of theplurality of couplings to a positive effective offset angle when the CVTis rotating in the forward direction, and adapted to adjust the radialposition of the plurality of couplings to a negative offset angle whenthe CVT is rotating in the reverse direction.

In one broad respect, embodiments disclosed herein may be directed to acontinuously variable transmission comprising a plurality of sphericalplanets between and in contact with two traction rings and a sun, eachplanet having a geometric center through which an x-axis, y-axis andz-axis intersect, wherein the plurality of geometric centers define apitch circle for the plurality of planets, wherein an axle extendsthrough a central bore of each of the plurality of spherical planets anddefines the z-axis and an axis of rotation. In some embodiments, thecontrol system comprises a plurality of trunnions, wherein each trunnionis coupled to each end of an axle and extends around a spherical planetto a coupling. In some embodiments, the plurality of trunnions areoriented at an offset angle (psi). In some embodiments, orientation ofthe plurality of traction planets such that the offset angle (psi) has apositive sign configures the CVT for operation in a first direction andorientation of the plurality of traction planets such that the offsetangle (psi) has a negative sign configures the CVT for operation in asecond direction. In some embodiments in which the plurality ofcouplings lead the spherical planets, the plurality of trunnions areoriented such that the offset angle (psi) has a positive sign foroperation in a forward direction and a negative sign for operation in areverse direction. In some embodiments in which the plurality ofcouplings trail the spherical planets, the plurality of trunnions areoriented such that the offset angle (psi) has a negative sign foroperation in a forward direction and a positive sign for operation in areverse direction. In some embodiments in which the axles are fixedaxially to the plurality of planets, axial translation of the pluralityof couplings imparts a skew condition on the plurality of tractionplanets to adjust a speed ratio of the CVT. In some embodiments in whichthe CVT further comprises a synchronizing ring coupled to the pluralityof couplings, axial translation of the synchronizing ring axiallytranslates the plurality of couplings to adjust the speed ratio of theCVT. The orientation of the plurality of trunnions is controlled byradial translation of the plurality of couplings. In some embodiments inwhich the couplings are fixed axially, an axial force applied to theplurality of axles imparts a skew condition on the plurality of tractionplanets to adjust a speed ratio of the CVT. In some embodiments in whicha synchronizer is coupled to at least one end of each axle, axialtranslation of the synchronizer axially translates the plurality ofaxles to adjust a speed ratio of the CVT. In some embodiments in whichthe synchronizer comprises a control disc positioned on one side of theCVT, the control disc comprises a plurality of slots and an end of eachaxle is coupled to a slot of the plurality of slots, wherein an axialforce is applied to the control disc in a first direction or a seconddirection opposite the first direction to adjust a speed ratio of theCVT. In some embodiments in which the synchronizer comprises a firstcontrol disc positioned on a first side of the plurality of slots and asecond control disc positioned on a second side of the plurality ofslots opposite the first control disc, an axial force is applied to thefirst control disc to apply an axial force to the axles in a firstdirection and an axial force is applied to the second control disc toapply an axial force to the axles in a second direction. In someembodiments in which the synchronizer comprises a plurality of arms witheach arm coupled to an axle of the plurality of axles, an axial forceapplied to the plurality of arms applies an axial force to the pluralityof axles to adjust a speed ratio of the CVT.

In another broad respect, embodiments disclosed herein may be directedto a method of controlling a continuously variable transmission (CVT)comprising a plurality of spherical planets between and in contact withtwo traction rings and a sun, each planet having a geometric centerthrough which an x-axis, y-axis and z-axis intersect, wherein theplurality of geometric centers define a pitch circle for the pluralityof planets, wherein an axle extends through a central bore of each ofthe plurality of spherical planets and defines the z-axis and an axis ofrotation for that planet, and a plurality of trunnions, wherein eachtrunnion is coupled to each end of an axle and extends around aspherical planet coupled to the axle. In some embodiments, the methodcomprises rotating the plurality of trunnions about their respectivez-axes to an offset angle (psi). An offset angle (psi) having a positivesign configures the CVT for operation in a first direction of rotation,and an offset angle (psi) having a negative sign configures the CVT foroperation in a second direction of rotation. In some embodiments, eachtrunnion is coupled to a trunnion extension via a coupling with multipledegrees of freedom, wherein the method comprises axially translating theplurality of trunnion extensions to impart a skew angle (zeta) on theplurality of traction planets to cause a change in a speed ratio of theCVT, whereby the couplings allow forces generated by the axialtranslation to tilt the planets. In some embodiments, each trunnion iscoupled to a trunnion extension with limited degrees of freedom, whereinthe method comprises applying an axial force to the plurality of axlesto impart the skew angle (zeta) on the plurality of traction planets tocause a change in a speed ratio of the CVT, whereby the couplings reactforces generated by the axial translation of the planets to tilt theplanets. In some embodiments, the method comprises axially fixing theplurality of couplings, wherein adjusting the speed ratio of the CVTcomprises applying an axial force to the plurality of axles. In someembodiments, the method comprises axially fixing the plurality of axlesto the plurality of traction planets, wherein adjusting the speed ratioof the CVT comprises axially translating the plurality of couplings. Insome embodiments, the method comprises determining a first direction ofrotation for the CVT; rotating the plurality of trunnions about theirrespective z-axes to a first offset angle (psi) for operation in thefirst direction of rotation; determining a change in direction ofrotation of the CVT to a second direction of rotation; and rotating theplurality of trunnions about their respective z-axes to a second offsetangle (psi) for operation in the second direction of rotation of theCVT. In some embodiments, the method comprises determining a firstdirection of operation; configuring the CVT for operation at a firstoffset angle (psi) for the first direction of rotation based on one ormore of a first user input, a first operating condition and a firstenvironmental condition; and configuring the CVT for operation at asecond offset angle (psi) for the first direction of rotation based onone or more of a second user input, a second operating condition and asecond environmental condition, wherein the first offset angle (psi) orthe second offset angle (psi) is selected for stable operation orsensitivity.

In another broad respect, embodiments disclosed herein may be directedto a control system for a continuously variable transmission (CVT)comprising a plurality of spherical planets between and in contact withtwo traction rings and a sun, each planet having a geometric centerthrough which an x-axis, y-axis and z-axis intersect, wherein theplurality of geometric centers define a pitch circle for the pluralityof planets, wherein an axle extends through a central bore of each ofthe plurality of spherical planets and defines the z-axis and an axis ofrotation. The control system comprises a controller communicativelycoupled to a plurality of sensors and further coupled to a plurality oftrunnions coupled to the plurality of axles, wherein each trunnion iscoupled to each end of an axle and extends around a spherical planetcoupled to that axle. The controller may receive signals related toperformance of the CVT, performance of a prime mover coupled to the CVT,signals related to performance of a vehicle associated with the CVT,signals related to the environment, and user inputs. The controller mayanalyze the signals and configure the CVT. In some embodiments, thecontroller may configure the CVT for forward or reverse rotation. Insome embodiments, the controller may configure the CVT for a desiredstability or sensitivity. In some embodiments, the controller maycompare the signals with values stored in memory, determine an operatingcondition is present and configure the CVT according to the operatingcondition. The operating condition may be a rollback condition, in whicha vehicle containing the CVT is in a rollback condition or about toencounter a rollback condition. In some embodiments, the controller mayanalyze the signals and determine a rollback condition is possible andconfigure the CVT for increased sensitivity. Configuring the CVT forincreased sensitivity may include adjusting trunnions to a smalleroffset angle (psi). In some embodiments, the smaller offset angle may beless than 10 degrees. In some embodiments, configuring the CVT forincreased sensitivity may include increasing the rate at which sensorssend signals to the controller. In some embodiments the controller mayconfigure the CVT for increased stability, which may include adjustingtrunnions to a higher offset angle (psi). Adjusting the trunnions maycomprise radially translating a control point for each trunnion to aradial position relative to a pitch circle or rotating the trunnions toan offset angle (psi). Each trunnion comprises a coupling, wherein acontrol point is defined along a line passing through the geometriccenter of each traction planet and the coupling for that tractionplanet, wherein a position of a plurality of control points radiallyoutside the pitch circle configures the CVT for a first direction,wherein a position of the plurality of control points radially insidethe pitch circle configures the CVT for a second direction opposite thefirst direction. An axial translation of the plurality of controlpoints, an axial force applied to the plurality of axles, or acombination thereof misaligns the plurality of axles relative to alongitudinal axis of the CVT to adjust a tilt angle of the plurality ofplanets. In some embodiments in which the plurality of couplings leadthe spherical planets, the controller may position the plurality ofcontrol points radially inward of the pitch circle for operation in aforward direction of rotation or radially outward of the pitch circlefor operation in a reverse direction of rotation. In some embodiments inwhich the plurality of couplings trail the spherical planets, acontroller may position the plurality of control points radially outwardof the pitch circle for operation in a forward direction of rotation orradially inward of the pitch circle for a reverse direction of rotation.In some embodiments, the plurality of axles are axially fixed to theplurality of planets and the CVT further comprises a plurality oftrunnion extensions coupled to the plurality of couplings and asynchronizing ring. A controller may control a radial position of theplurality of couplings by radial translation of the plurality oftrunnion extensions. A controller may command an axial translation ofthe synchronizing ring to axially translate the plurality of couplingsto adjust the speed ratio of the CVT. In some embodiments, the couplingsare fixed axially, and a controller may command an axial force beapplied to the plurality of axles to impart a non-zero skew condition tothe plurality of planets. The non-zero skew condition causes the CVT toadjust a tilt angle of the plurality of spherical planets. In someembodiments, a synchronizer is coupled to at least one end of each axle,wherein a controller commanding an axial force applied to thesynchronizer misaligns the plurality of axles to adjust a tilt angle ofthe plurality of traction planets. In some embodiments, the synchronizercomprises a control disc positioned on one side of the CVT. The controldisc has a plurality of slots and an end of each axle is coupled to aslot of the plurality of slots. An axial force applied to the controldisc in a first direction or a second direction opposite the firstdirection imparts a non-zero skew condition to adjust a tilt angle ofthe plurality of traction planets. In some embodiments, the synchronizercomprises a first control disc positioned on a first side of theplurality of slots and a second control disc positioned on a second sideof the plurality of slots opposite the first control disc, wherein acontroller commanding an axial force applied to the first control discapplies an axial force to the axles in a first direction to impart anon-zero skew condition to adjust a tilt angle of the plurality oftraction planets toward underdrive, or an axial force applied to thesecond control disc applies an axial force to the axles in a seconddirection to impart a non-zero skew condition to adjust a tilt angle ofthe plurality of traction planets toward overdrive. In some embodiments,the synchronizer comprises a plurality of arms. Each rigid member iscoupled to an axle of the plurality of axles, wherein an axial forceapplied to the plurality of arms applies an axial force to the pluralityof axles to adjust a tilt angle of the plurality of traction planets.

In another broad respect, embodiments disclosed herein may be generallydirected to a method of controlling a continuously variable transmission(CVT) comprising a plurality of spherical planets between and in contactwith two traction rings and a sun, each planet having a geometric centerthrough which an x-axis, y-axis and z-axis intersect, wherein theplurality of geometric centers define a pitch circle for the pluralityof planets, wherein an axle extends through a central bore of each ofthe plurality of spherical planets and defines the z-axis and an axis ofrotation for that planet, and a plurality of trunnions, wherein eachtrunnion is coupled to each end of an axle and extends around aspherical planet coupled to that axle, wherein each trunnion comprises acoupling, wherein a control point is defined along a line passingthrough the geometric center of each traction planet and the couplingfor that traction planet. In some embodiments, rotating the plurality oftrunnions about their respective z-axes to an offset angle (psi)comprises determining a control scheme and rotating the plurality oftrunnions to the offset angle (psi) based on the control scheme. In someembodiments, the plurality of trunnions are rotated to a larger angleassociated with a control scheme selected for stable operation or arerotated to a smaller angle associated with a control scheme selected forincreased sensitivity.

In another broad respect, embodiments disclosed herein may be generallydirected to a control system for a ball planetary continuously variabletransmission (CVT) comprising a plurality of spherical planets betweenand in contact with two traction rings and a sun, each planet having ageometric center through which an x-axis, y-axis and z-axis intersect,wherein the plurality of geometric centers define a pitch circle for theplurality of planets, wherein an axle extends through a central bore ofeach of the plurality of spherical planets and defines the z-axis and anaxis of rotation. In some embodiments, the control system comprises aplurality of trunnions coupled to the plurality of axles, wherein eachtrunnion comprises a first link coupled to a first end of an axle, asecond link coupled to a second end of the axle, and a center linkcoupled to the first link and the second link. A first actuator mayconfigure the plurality of trunnions to an offset angle (psi) relativeto the pitch circle. A second actuator may rotate the center link. Acontroller communicatively coupled to the actuator and a plurality ofsensors may be configured to receive signals from the plurality ofsensors, determine a direction of rotation for the CVT, send a firstsignal to the first actuator to adjust the offset angle (psi) of theplurality of trunnions and send a signal to the second actuator toimpart a skew angle (zeta) on the plurality of axles to adjust a tiltangle. In some embodiments, if the plurality of trunnions lead theplurality of planets and the offset angle (psi) is positive, the CVT isconfigured for operation in a forward direction. In some embodiments, ifthe plurality of trunnions trail the plurality of planets and the offsetangle (psi) is negative, the CVT is configured for operation in forwarddirection. A speed ratio of the CVT may be based on the tilt angle, theskew angle and the offset angle. The controller may receive signalsrelated to performance of the CVT, performance of a prime mover coupledto the CVT, signals related to performance of a vehicle associated withthe CVT, signals related to the environment, and user inputs. Thecontroller may analyze the signals and configure the CVT. In someembodiments, the controller may configure the CVT for forward or reverserotation. In some embodiments, the controller may configure the CVT fora desired stability or sensitivity. In some embodiments, the controllermay compare the signals with values stored in memory, determine anoperating condition is present and configure the CVT according to theoperating condition. The operating condition may be a rollbackcondition, in which a vehicle containing the CVT is in a rollbackcondition or about to encounter a rollback condition. In someembodiments, the controller may analyze the signals and determine arollback condition is possible and configure the CVT for increasedsensitivity. In some embodiments, the controller is further configuredto change the offset angle (psi) in response to determining a change inthe direction of rotation or receiving an input to change the directionof rotation. In some embodiments, the controller is further configuredto adjust the offset angle (psi) to have a larger magnitude for a firstcontrol scheme for stable control or to have a smaller magnitude for asecond control scheme for increased sensitivity.

In another broad respect, embodiments disclosed herein may be generallydirected to a ball planetary continuously variable transmission (CVT)comprising a plurality of spherical planets between and in contact withtwo traction rings and a sun, each planet having a geometric centerthrough which an x-axis, y-axis and z-axis intersect, wherein theplurality of geometric centers define a pitch circle for the pluralityof planets, wherein an axle extends through a central bore of each ofthe plurality of spherical planets and defines the z-axis and an axis ofrotation, and a control system. The control system may comprise aplurality of trunnions coupled to the plurality of axles, a firstactuator for configuring the plurality of trunnions to an offset angle(psi) relative to the pitch circle, a second actuator for rotating thecenter link and a controller communicatively coupled to the actuator anda plurality of sensors. In some embodiments, each trunnion comprises afirst link coupled to a first end of an axle, a second link coupled to asecond end of the axle, and a center link coupled to the first link andthe second link. In some embodiments, the controller is configured toreceive signals from the plurality of sensors, determine a direction ofrotation for the CVT, send a first signal to the first actuator toadjust the offset angle (psi) of the plurality of trunnions, and send asignal to the second actuator to impart a skew angle (zeta) on theplurality of axles to adjust a tilt angle. In some embodiments, if theplurality of trunnions lead the plurality of planets and the offsetangle (psi) is positive, a controller may configure the CVT foroperation in a forward direction. In some embodiments, if the pluralityof trunnions trail the plurality of planets and the offset angle (psi)is negative, a controller may configure the CVT for operation in forwarddirection. In some embodiments, a speed ratio of the CVT may be based onthe tilt angle, the skew angle and the offset angle. In someembodiments, the first link and the second link comprise rigid members.

In another broad respect, embodiments disclosed herein may be generallydirected to a control system for a continuously variable transmission(CVT) comprising a plurality of spherical planets between and in contactwith two traction rings and a sun, each planet having a geometric centerthrough which an x-axis, y-axis and z-axis intersect, wherein theplurality of geometric centers define a pitch circle for the pluralityof planets, wherein an axle extends through a central bore of each ofthe plurality of spherical planets and defines the z-axis and an axis ofrotation. The control system comprises a first carrier member located ona first side of the CVT, a first plurality of arms on the first side ofthe CVT, a second carrier member located on a second side of the CVT, asecond plurality of arms, a first actuator for rotating one or more ofthe first carrier and the second carrier to an angular orientation ofthe first carrier relative to the second carrier member, and acontroller communicatively coupled to the actuator and a plurality ofsensors. A first end of each arm of the first plurality of arms iscoupled to a first end of an axle and a second end of each arm of thefirst plurality of arms is coupled to the first carrier member. A firstend of each arm of the second plurality of arms is coupled to a secondend of an axle and a second end of each arm of the second plurality ofarms is coupled to the second carrier member. The controller configuredto receive signals from the plurality of sensors and command the firstactuator to rotate the first carrier member relative to the secondcarrier member, wherein rotation of the first carrier member relative tothe second carrier member imparts a skew condition on the plurality ofplanets to tilt the plurality of axles to a tilt angle associated with aspeed ratio for the CVT. In some embodiments, the first plurality ofarms are movable relative to the first carrier member and the secondplurality of arms are movable relative to the second carrier member andthe control system further comprises a second actuator for radiallyrotating one or more of the first plurality of arms and the secondplurality of arms to an offset angle (psi) to configure the CVT foroperation in a forward direction of rotation or reverse direction ofrotation. The controller may receive signals related to performance ofthe CVT, performance of a prime mover coupled to the CVT, signalsrelated to performance of a vehicle associated with the CVT, signalsrelated to the environment, and user inputs. The controller may analyzethe signals and configure the CVT. In some embodiments, the controllermay configure the CVT for forward or reverse rotation. In someembodiments, the controller may configure the CVT for a desiredstability or sensitivity. In some embodiments, the controller maycompare the signals with values stored in memory, determine an operatingcondition is present and configure the CVT according to the operatingcondition. The operating condition may be a rollback condition, in whicha vehicle containing the CVT is in a rollback condition or about toencounter a rollback condition. In some embodiments, the controller mayanalyze the signals and determine a rollback condition is possible andconfigure the CVT for increased sensitivity. In some embodiments, thecontroller is further configured to change the offset angle (psi) inresponse to determining a change in the direction of rotation orreceiving an input to change the direction of rotation. In someembodiments, the controller is further configured to adjust the offsetangle (psi) to have a larger magnitude for a first control scheme forstable control or to have a smaller magnitude for a second controlscheme for increased sensitivity. In some embodiments, the controller isconfigured to receive a user input for one or more of a direction ofrotation, a control mode, and a speed ratio. In some embodiments,orientation of the first plurality of arms to a positive first offsetangle (psi) relative to the first carrier member and orientation of thesecond plurality of arms to a positive second offset angle (psi)relative to the second carrier member configures the CVT for operationin a first direction of rotation, wherein orientation of the firstplurality of arms to a negative first offset angle (psi) relative to thefirst carrier member and orientation of the second plurality of arms toa negative second offset angle (psi) relative to the second carriermember configures the CVT for operation in a second direction ofrotation. In some embodiments, if the first carrier member and thesecond carrier member lead the plurality of axles, orientation of thefirst plurality of arms to a positive first offset angle (psi) andorientation of the second plurality of arms to a positive second offsetangle (psi) configures the CVT for operation in forward direction andorientation of the first plurality of arms to a negative first offsetangle (psi) and orientation of the second plurality of arms to anegative second offset angle (psi) configures the CVT for operation inreverse direction, and wherein if the first carrier member and thesecond carrier member trail the plurality of axles, orientation of thefirst plurality of arms to a positive first offset angle (psi) andorientation of the second plurality of arms to a positive second offsetangle (psi) configures the CVT for operation in reverse direction andorientation of the first plurality of arms to a negative first offsetangle (psi) and orientation of the second plurality of arms to anegative second offset angle (psi) configures the CVT for operation inforward direction. In some embodiments, at least one of the firstplurality of arms and the second plurality of arms is formed as aresilient member. In some embodiments, at least one of the firstplurality of arms and the second plurality of arms is formed withdirectional resiliency.

In another broad respect, embodiments disclosed herein may be generallydirected to a continuously variable transmission (CVT) comprising aplurality of spherical planets between and in contact with two tractionrings and a sun, each planet having a geometric center through which anx-axis, y-axis and z-axis intersect, wherein the plurality of geometriccenters define a pitch circle for the plurality of planets, wherein anaxle extends through a central bore of each of the plurality ofspherical planets and defines the z-axis and an axis of rotation. Insome embodiments, orientation of the first plurality of arms to apositive first offset angle (psi) relative to the first carrier memberand orientation of the second plurality of arms to a positive secondoffset angle (psi) relative to the second carrier member configures theCVT for operation in a first direction of rotation. In some embodiments,orientation of the first plurality of arms to a negative first offsetangle (psi) relative to the first carrier member and orientation of thesecond plurality of arms to a negative second offset angle (psi)relative to the second carrier member configures the CVT for operationin a second direction of rotation. In some embodiments, if the firstcarrier member and the second carrier member lead the plurality ofaxles, orientation of the first plurality of arms to a positive firstoffset angle (psi) and orientation of the second plurality of arms to apositive second offset angle (psi) configures the CVT for operation inforward direction and orientation of the first plurality of arms to anegative first offset angle (psi) and orientation of the secondplurality of arms to a negative second offset angle (psi) configures theCVT for operation in reverse direction. In some embodiments, if thefirst carrier member and the second carrier member trail the pluralityof axles, orientation of the first plurality of arms to a positive firstoffset angle (psi) and orientation of the second plurality of arms to apositive second offset angle (psi) configures the CVT for operation inreverse direction and orientation of the first plurality of arms to anegative first offset angle (psi) and orientation of the secondplurality of arms to a negative second offset angle (psi) configures theCVT for operation in forward direction. In some embodiments, at leastone of the first link and the second link is formed as a resilientmember. In some embodiments, at least one of the first link and thesecond link is formed with directional resiliency.

In another broad respect, embodiments disclosed herein may be generallydirected to a method of adjusting a speed ratio of a continuouslyvariable transmission (CVT) comprising a plurality of spherical planetsbetween and in contact with two traction rings and a sun, each planethaving a geometric center through which an x-axis, y-axis and z-axisintersect, wherein the plurality of geometric centers define a pitchcircle for the plurality of planets, wherein an axle extends through acentral bore of each of the plurality of spherical planets and definesthe z-axis and an axis of rotation. In some embodiments, the methodcomprises rotating a first carrier member relative to a second carriermember, wherein the first carrier member is coupled to a first pluralityof arms, wherein each arm of the first plurality of arms is coupled to afirst end of an axle of a traction planet, wherein the second carriermember is coupled to a second plurality of arms, wherein each arm of thesecond plurality of arms coupled to a second end of the axle of atraction planet, wherein rotating the first carrier member relative tothe second carrier member misaligns the plurality of axes of rotationrelative to a longitudinal axis of the CVT to change a speed ratio ofthe CVT. In some embodiments, the method includes adjusting an offsetangle (psi) for the first plurality of arms and the second plurality ofarms, wherein a positive offset angle (psi) configures the CVT foroperation in a first direction of rotation, wherein a negative offsetangle (psi) configures the CVT for operation in a second direction ofrotation. In some embodiments, adjusting an offset angle (psi) for thefirst plurality of arms and the second plurality of arms comprisesadjusting a magnitude of the offset angle (psi). In some embodiments,the magnitude is based on a control scheme, wherein the offset angle(psi) is adjusted to a larger magnitude for stable control or adjustedto a smaller magnitude for increased sensitivity. In some embodiments,one or more of the control scheme, the direction of rotation and thespeed ratio are user input received from a user interface.

These, and other, aspects of the disclosed technology will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. The followingdescription, while indicating various embodiments of the disclosedtechnology and numerous specific details thereof, is given by way ofillustration and not of limitation. Many substitutions, modifications,additions or rearrangements may be made within the scope of thedisclosed technology, and the disclosed technology includes all suchsubstitutions, modifications, additions or rearrangements.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings accompanying and forming part of this specification areincluded to depict certain aspects of the disclosed technology. Aclearer impression of the disclosed technology, and of the componentsand operation of systems provided with the disclosed technology, willbecome more readily apparent by referring to the exemplary, andtherefore non-limiting, embodiments illustrated in the drawings, whereinidentical reference numerals designate the same components. Note thatthe features illustrated in the drawings are not necessarily drawn toscale.

FIG. 1A depicts a schematic diagram of a continuously variabletransmission relative to global and planet-centered coordinate systems;

FIGS. 1B and 1C depict schematic diagrams of planet-centered coordinatesystems and relative coordinate systems, illustrating relationshipsbetween skew and tilt in ball-planetary continuously variabletransmissions;

FIG. 1D depicts a schematic diagram of certain kinematic relationshipsbetween contacting components of a CVT, illustrating how the inducementof a skew condition generates forces that tend to adjust a tilt angle;

FIG. 1E depicts a generalized, representative traction curve that can beapplied at each of contact areas 1, 2, 3, illustrating a relationshipbetween the traction coefficient μ and the relative velocity betweencontacting components;

FIGS. 1F and 1G depict front and top schematic diagrams, illustratingtraction forces exerted relative to a planet under non-zero skewconditions;

FIGS. 2A-2J depict partial perspective, side and front views of a CVT,illustrating one embodiment of a control system capable of operation inforward direction and reverse direction;

FIGS. 3A-3J depict front partial views of a CVT, illustrating oneembodiment of a control system capable of operation in forward directionand reverse direction; and

FIGS. 4A-4O depict partial perspective, side and front views of a CVT,illustrating one embodiment of a control system capable of operation inforward direction and reverse direction.

DETAILED DESCRIPTION OF CERTAIN ILLUSTRATIVE EMBODIMENTS

Systems and methods and advantageous details thereof are explained morefully with reference to the non-limiting embodiments that areillustrated in the accompanying drawings and detailed in the followingdescription. Descriptions of well-known starting materials, processingtechniques, components and equipment are omitted so as not tounnecessarily obscure the disclosed technology in detail. It should beunderstood, however, that the detailed description and the specificexamples, while indicating certain embodiments of the disclosedtechnology, are given by way of illustration only and not by way oflimitation. Various substitutions, modifications, additions and/orrearrangements within the spirit and/or scope of this disclosure willbecome apparent to those skilled in the art from this disclosure.

Embodiments disclosed herein comprise ball-planetary continuouslyvariable transmissions (CVTs) in which a plurality of planets areinterposed between and in contact with traction rings and a sun, inwhich tilting of the planets changes a speed ratio of the CVT.

Speed ratio may vary between underdrive and overdrive. In underdrive,power enters a first traction ring with a first torque and a first speedand is transferred through planets to a second traction ring with asecond torque higher than the first torque and a second speed lower thanthe first speed. In overdrive, power enters the first traction ring witha first torque and a first speed and is transferred through planets tothe second traction ring with a lower torque greater than the firsttorque and a second speed higher than the first speed.

Each planet has a geometric center, with an x-axis, y-axis and z-axisfor that planet intersecting at its geometric center. The geometriccenters of planets arranged angularly around a longitudinal axiscollectively define a pitch circle for the plurality of planets.

Each planet is coupled to an axle. Each axle defines an axis ofrotation, which is aligned with a z-axis of a planet. Tilting axles to anon-zero tilt angle (gamma) causes contact points between planets andtraction rings to change, adjusting a speed ratio of a CVT. Thoseskilled in the art will appreciate that for a change in speed ratio of aCVT, there is also a reciprocal change in torque ratio. Thus, a changethat results in an increase in speed ratio will have a decrease intorque ratio, and a change that results in a decrease in speed ratiowill have an increase in torque ratio.

As used herein, the terms “axial”, “axially” and the like refer to adirection along or parallel to a longitudinal axis of the CVT.

As used herein, the terms “radial”, “radially” and the like refer to adirection perpendicular to a longitudinal axis of the CVT.

For ease of understanding, direction 25 refers to a forward rotation(also referred to as a design direction) and direction 26 refers toreverse rotation, and in the embodiments illustrated power istransferred from first traction ring 102 to second traction ring 104.

Embodiments disclosed herein may include a control system configurableto adjust a CVT, such as CVT 200, to a target speed ratio for operationin a forward direction or a reverse direction, including maintaining aspeed ratio during a switch between operation in forward direction andoperation in a reverse direction, and operate according to a controlscheme for increased stability or sensitivity. FIGS. 2A-2J depict frontand side views of CVT 200 comprising a plurality of planets 108interposed between traction rings 102, 104 and sun 110, illustrating CVT200 configured for operation at 1:1, underdrive and overdrive speedratios in forward and reverse directions.

As depicted in FIGS. 2A-2J, planets 108 are coupled to tiltable axles103 that define axes of rotation 106 which are coaxial with the z-axesfor planets 108. Axles 103 are coupled to planets 108 such the planets108 may rotate about axes of rotation 106. If present, bearings 107 mayfacilitate rotation of axles 103 in trunnions 220. In embodimentsdepicted in FIGS. 2A-2J, bearings 107 allow axles 103 to rotate relativeto trunnions 220 but axially fix axles 103 relative to trunnions 220.

Trunnions 220 may be machined or otherwise formed as rigid members forcoupling to axles 103 to allow a control system to adjust an orientationof planets 108 in operation to adjust a speed ratio in forward directionand reverse direction. Trunnions 220 are rotatably coupled to axles 103on either side of planets 108. FIGS. 2A-2J depict embodiments oftrunnions 220 formed as arcuate rigid members. However, trunnions 220may be formed having any shape capable of coupling to both ends of axle103 and not contacting planets 108. FIGS. 2A-2J depict embodiments inwhich trunnions 220 are formed such that axles 103 and bearings 107 maybe accessible via openings 223. However, trunnions 220 may be formedwith smaller openings 223 such that only axles 103 are accessible,including without openings 223. Trunnions 220 are formed having aneffective length defined along line 23 between a first intersection A ofline 23 and radial line 20 and a second intersection B of line 23 andradial line 22. Offset 40 may result in an angular offset, allowclearance between trunnions 220 and planets 108, allow for ease inassembly, and other advantages.

Couplings 215 on trunnions 220 allow trunnions 220 one or more degreesof freedom relative to trunnion extensions 213. FIGS. 2A-2J depict CVT200 with one embodiment of coupling 215 as a ball and socket coupling,which allows for multiple degrees of freedom. Other shapes andconfigurations of coupling 215 may be used to provide fewer or moredegrees of freedom.

Trunnion extensions 213 may be coupled to ring 212 such that axialtranslation and circumferential rotation of trunnion extensions 213 arefixed relative to ring 212, but radial translation of trunnionextensions 213 and rotation about radial lines 22 are possible. Forexample, as depicted in FIGS. 2A-2J, trunnion extensions 213 arecylindrical and ring 212 is formed with openings 216 such that trunnionextensions 213 are restricted to radial translation along radial lines22 and/or rotation about radial lines 22.

For purposes of describing concepts related to embodiments such as CVT200, FIGS. 2B-2J refer to point A and point B, which are approximatelocations. For example, point A is depicted as coincident with theintersection of axis of rotation 106 and a midplane of axle 103, but theexact location of point A will depend on factors such as tilt angle(gamma) 28, skew angle (zeta) 27, offset angle (psi) 24, the input speedof first traction ring 102, the output speed of second traction ring104, a friction coefficient between components, the presence andcharacteristics of a traction fluid. Thus, at 1:1 ratio, point A may begenerally coincident with the intersection of axis of rotation 106 and amidplane of axle 103. At full underdrive or full overdrive, point A maynot be coincident with the intersection of axis of rotation 106 and amidplane of axle 103. Similarly, point B is depicted as coincident withan intersection of radial line 22 and line 23 passing through ageometric center of planets 108, but the exact position of point B willdepend on factors such as tilt angle (gamma) 28, skew angle (zeta) 27,offset angle (psi) 24, the input speed of first traction ring 102, theoutput speed of second traction ring 104, a friction coefficient betweencomponents, and the presence and characteristics of a traction fluid.Accordingly, when referring to point A or point B in the accompanyingfigures, an arrow depicts an approximate location of point A or point B.

Radial translation or axial translation of trunnion extensions 213 maybe controlled by an actuator. In some embodiments, ring 212 may becoupled to one or more actuators (not shown). An actuator may axiallytranslate ring 212 or radially translate trunnion extensions 213. Anactuator may be actuated manually, such as by a person adjusting a leveror twisting a grip, or an actuator may be controlled electronically,such as by a controller operating a set of instructions andcommunicatively coupled to an electronic servo, encoder, or hydraulicpump.

Axial translation of ring 212 distance D axially translates eachtrunnion extension 213 distance D to rotate trunnion 220, axle 103 andplanet 108 about point A. Multiple degrees of freedom associated withcoupling 215 allow ring 212 to translate axially but allow each trunnion220, axle 103 or planet 108 to be rotated about its respective y-axis.

In operation, an actuator (controlled manually or by an electroniccontroller) may orient trunnions 220 to an offset angle (psi) 24relative to pitch circle 12. Offset angle (psi) 24 may have a first sign(e.g., positive) during forward rotation and an opposite sign (e.g.,negative) during reverse rotation. For embodiments such as thosedepicted with respect to FIGS. 2A-2J in which couplings 215 lead planets108 in forward rotation and trail planets 108 in reverse rotation, apositive offset angle (psi) (that is, coupling 215 is translatedradially inward to orient trunnions 220 to a positive offset angle (psi)24 relative to pitch circle 12) configures CVT 200 for operation in aforward direction, and a negative offset angle (psi) 24 (that is,coupling 215 is translated radially outward to orient trunnions 220 to anegative offset angle (psi) 24 relative to pitch circle 12) configuresCVT 200 for operation in a reverse direction. Offset angle (psi) 24 oftrunnions 220 may be changed independently or concurrently with a changein axial translation D of couplings 215 or skew angle (zeta) 27 of axles103.

FIGS. 2A-2J depict embodiments at 1:1, underdrive and overdrive, inforward rotation and reverse rotation. Each trunnion 220 is movablycoupled to trunnion extension 213 coupled to ring 212. Ring 212 may betranslated axially relative to longitudinal axis 15 a distance D tomisalign axles 103 (and therefore axes of rotation 106) of planets 108.Skew angle (zeta) 27 in conjunction with axial constraint of planets 108results in spin-induced forces causing axles 103 to tilt to tilt angle(gamma) 28. Skew angle (zeta) 27 to which axles 103 are misaligned maybe determined based on an axial translation of synchronizing ring 212relative to center plane 14 of CVT 200 as defined by the geometriccenters of planets 108. In some embodiments, offset angle (psi) 24depends on a distance that trunnion extensions 213 are translatedradially outward or inward of pitch circle 12.

As depicted in FIGS. 2A-2C and 2F-2H, center plane 13 of carrier 212 iscoplanar with center plane 14 of CVT 200 such that a distance D betweencenter plane 13 of carrier 212 and center plane 14 of CVT 200 is zero.Under these conditions, skew angle (zeta) 27 applied to planets 108 iszero. As axles 103 react to unbalanced forces and tilt to an equilibriumstate, tilt angle (gamma) 28 adjusts to zero, and the speed ratio of CVT200 is 1:1 (minus any losses). As depicted in FIGS. 2A-2D, when coupling215 is radially inward of pitch circle 12, trunnions 220 are oriented toa positive offset angle (psi) 24 and CVT 200 is configured for forwardrotation 25.

As depicted in FIG. 2D, synchronizing ring 212 may be translateddistance D toward second traction ring 104 such that trunnion extension213 and coupling 215 are translated axially toward second traction ring104. Since planets 108 are axially constrained but capable of rotationabout their respective y-axes, an axial translation of couplings 215imparts a skew angle (zeta) 27 on axles 103, with skew angle (zeta) 27being a function of one or more of distance D of axial translation ofsynchronizing ring 212, width 222 of trunnions 220, and the length ofline AB. Tilt angle (gamma) 28 is a function of one or more of skewangle (zeta) 27 and offset angle (psi) 24. FIG. 2D depicts CVT 200 witha positive offset angle (psi) 24 and configured in underdrive forforward rotation 25.

As depicted in FIG. 2E, synchronizing ring 212 may be translated axiallytoward first traction ring 102 such that trunnion extensions 213 andcouplings 215 are translated axially toward first traction ring 102. Ifaxles 103 are axially fixed relative to planets 108, the axialtranslation imparts skew angle (zeta) 27 on trunnions 220, with skewangle (zeta) 27 being a function of one or more of distance D of axialtranslation of trunnion extensions 215, width 222 of trunnions 220, andthe length of line AB. Rotation of each planet 108 about a correspondingy-axis results in spin-induced (traction) forces on that planet 108. Asthese forces are exerted on planets 108, friction and other forces inCVT 200 act to return CVT 200 to a balanced state. If trunnion extension213 is maintained axial distance D from center plane 14 of CVT 200,returning to a balanced state results in planet axles 103 (and thereforeplanets 108) tilting to a new tilt angle (gamma) 28 corresponding to azero-skew condition. Embodiments described herein may continuouslyadjust distance D to adjust a speed ratio of CVT 200. Tilt angle (gamma)28 is a function of one or more of skew angle (zeta) 27 and offset angle(psi) 24. FIG. 2E depicts CVT 200 with a positive offset angle (psi) 24and configured in overdrive for forward rotation 25.

As depicted in FIGS. 2F-2H, center plane 13 of carrier 212 may betranslated axially to a position that is coplanar with center plane 14of CVT 200 such that a distance D between center plane 13 of carrier 212and center plane 14 of CVT 200 is zero. Under these conditions, skewangle (zeta) 27 is zero, which may be characterized as having zero orminimal spin-induced forces. A lack of spin-induced forces causesplanets 108 to tilt to an equilibrium position in which tilt angle(gamma) 28 is zero, and the speed ratio of CVT 200 is 1:1 (minus anylosses). As depicted in FIGS. 2F-2H, when coupling 215 is radiallyoutward of pitch circle 12 of planets 108, offset angle (psi) 24 isnegative and CVT 200 is configured for reverse direction 26.

As depicted in FIG. 2J, synchronizing ring 212 may be translateddistance D toward second traction ring 104 such that trunnion extension213 and coupling 215 are translated axially toward second traction ring104. If axles 103 are axially fixed relative to planets 108, the axialtranslation imparts skew angle (zeta) 27 on trunnions 220, with skewangle (zeta) 27 being a function of one or more of distance D of axialtranslation of trunnion extensions 215, width 222 of trunnions 220, andthe length of line AB. Rotation of each planet 108 about a correspondingy-axis results in spin-induced (traction) forces on that planet 108. Asthese forces are exerted on planets 108, friction and other forces inCVT 200 act to return CVT 200 to a balanced state. If trunnionextensions 213 are maintained axial distance D from center plane 14 ofCVT 200, returning to a balanced state results in planet axles 103 (andtherefore planets 108) tilting to a new tilt angle (gamma) 28corresponding to a zero-skew condition. Embodiments described herein maycontinuously adjust distance D to adjust a speed ratio of CVT 200. Tiltangle (gamma) 28 is a function of one or more of skew angle (zeta) 27and offset angle (psi) 24. FIG. 2I depicts CVT 200 with a negativeoffset angle (psi) 24 and configured in overdrive for operation inreverse direction 26.

As depicted in FIG. 2J, synchronizing ring 212 may be translated axiallytoward first traction ring 102 such that trunnion extension 213 andcoupling 215 are translated axially toward first traction ring 102. Ifaxles 103 are axially fixed relative to planets 108, the geometriccenter of planets 108 may serve as control points. The axial translationrotates trunnions 220 to skew angle (zeta) 27, with skew angle (zeta) 27being a function of one or more of distance D of axial translation oftrunnion extensions 215, width 222 of trunnions 220, and the length ofline AB. Rotation of each planet 108 about a corresponding y-axisresults in spin-induced (traction) forces on that planet 108. As theseforces are exerted on planets 108, friction and other forces in CVT 200act to return CVT 200 to a balanced state. If trunnion extensions 213are maintained axial distance D from center plane 14 of CVT 200,returning to a balanced state results in planet axles 103 (and thereforeplanets 108) tilting to a new tilt angle (gamma) 28 corresponding to azero-skew condition. Embodiments described herein may continuouslyadjust distance D to adjust a speed ratio of CVT 200. Tilt angle (gamma)28 is a function of one or more of skew angle (zeta) 27 and offset angle(psi) 24. FIG. 2I depicts CVT 200 with a negative offset angle (psi) 24and configured in underdrive for operation in reverse rotation 26.

Offset angle (psi) 24 may be adjusted to any angle within a range ofpositive and negative angles. In some embodiments, a range of offsetangle (psi) 24 may be selected to allow operation of CVT 200 in forwardor reverse direction and capable of operating according to differentcontrol schemes. Persons skilled in the art will appreciate thatrotation of trunnions 220 to new offset angles (psi) 24 results in oneor more of the following states:

-   -   for increased offset angle (psi) 24, CVT 200 becomes more stable        but sensitivity is decreased, resulting in adjusting speed        ratios taking more time or adjusting at a slower rate;    -   for offset angles (psi) that approach zero, the speed at which        speed ratios may be adjusted may be faster, but the stability of        CVT 200 is diminished.

For example, a range may include larger angles (for example, but notlimited to, up to +15 degrees) to allow CVT 200 to use a control schemefor stable operation during forward rotation or for increasedsensitivity, and may include larger angles (for example, but not limitedto, up to −15 degrees) to also allow CVT 200 to use a control scheme forstable operation or for increased sensitivity during operation inreverse direction 26. In other embodiments, a range may include largerangles (for example, but not limited to, up to +15 degrees) to allow CVT200 to use a control scheme for stable operation during forward rotationor for increased sensitivity, but may include smaller angles (forexample, but not limited to, up to −5 degrees) to allow CVT 200 to use acontrol scheme for increased sensitivity during operation in reversedirection 26.

Adjustment of CVT 200 may involve changing the sign of offset angle(psi) 24. In some embodiments, radial translation of couplings 215 froma position radially outward of pitch circle 12 of planets 108 to aposition radially inward of pitch circle 12 of planets 108 (or viceversa) changes the sign of offset angle (psi) 24 from positive tonegative or negative to positive, respectively. As depicted in FIGS.2E-2H, when couplings 215 are radially outward of pitch circle 12 ofplanets 108, offset angle (psi) 24 is negative, and CVT 200 isconfigured for operation in reverse direction 26.

Embodiments may change skew angle (zeta) 27 to accommodate changes inoffset angle (psi) 24. For example, if CVT 200 is operating in forwarddirection 25 in underdrive and CVT 200 needs to be operating in reversedirection 26 in underdrive, embodiments may configure CVT 200 bychanging offset angle (psi) 24 from a first sign (e.g., positive) to asecond sign (e.g., negative) and axially translating couplings 215 froma first side of center plane 14 of CVT 200 to a second side of centerplane 14 of CVT 200 opposite the first side.

As described in relation to FIGS. 2A-2J, adjusting a CVT may includeaxial constraint between a planet and a trunnion and adjustment may beaccomplished by axial translation of a trunnion extension. Variationsare possible. For example, in some embodiments, couplings 215 may befixed axially and adjustment of CVT 200 may be accomplished by axialtranslation of axles 103 relative to planets 108. In these embodiments,bearings 107, axles 103, or planets 108 may allow for axial translationof planets 108 relative to axles 103. In some embodiments, an actuatormay be coupled to a torus plate, a control disc, spider arms, or othersynchronizer (not shown) coupled to axles 103 or trunnions 220. Theactuator may translate the synchronizer to impart an axial translationof axles 103 relative to planets 108. Axial translation of axles 103relative to planets 108 while restricting axial movement of coupling 215will impart a non-zero skew angle (zeta) 24 on planets 108, adjustingaxles 103 to a target tilt angle (gamma) 28 such that CVT 200 operatesat a target speed ratio. In some embodiments, a synchronizer maycomprise a single control disc coupled to one end of axles 103. In otherembodiments, a synchronizer may comprise a first control disc coupled toa first end of axles 103 and a second control disc coupled to a secondend of axles 103. The pair of control discs may be coupled such thataxial translation of one control disc equals axial translation of thesecond control disc.

Embodiments disclosed herein may refer to a CVT with a control systemcapable of controlling a tilt angle using two carrier halves coupled tolinks. In these embodiments, one or both carrier halves are rotatableindependently or collectively to an angular position (beta) to impart askew angle (zeta) on planet axles to adjust a tilt angle (gamma) for aplurality of planets coupled to the planet axles. Furthermore, to enableforward and reverse rotation, the control system may control an offsetangle (psi) of the links) for operation in forward direction and reversedirections or for a selected sensitivity.

FIGS. 3A-3J depict CVT 300 in which two carrier halves 310A, 310B may berotated relative to each other to angular position (beta) 29, impartinga non-zero skew angle (zeta) 27 on axles 103 to cause axles 103 toadjust a speed ratio of CVT 300. A non-zero skew angle (zeta) 27 causesa non-zero skew condition, and spin-induced (traction) forces generatedby the geometry and configuration of CVT 300 adjusts a tilt angle(gamma) 28 of axles 103. During forward rotation, links 321 may berotated about axes of rotation 106 (coaxial with the z-axes of axles103) to a positive offset angle (psi) as depicted in FIGS. 3A-3E, andduring reverse rotation, links 321 may be rotated about axes of rotation106 to a negative offset angle (psi) as depicted in FIGS. 3F-3J.

Links 321 comprise a first end coupled to axles 103 and a second endcoupled to pins 312. Pins 312 may translate along slots 313 in carrierarms 311A on carrier half 310A and pins 312 may translate along slots313 in carrier arms 311B on carrier half 310B. Pins 312 may be locatedat a first radial position in slots 313 in carrier arms 311A and pins312 may be located at a second radial position in slots 313 in carrierarms 311B. Thus, a first offset angle (psi) 24A on a first side of CVT300 and a second offset angle (psi) 24B on a second side of CVT 300 maybe, but are not required to be, the same angle, or even the same sign.The difference between first offset angle (psi) 24A and second offsetangle (psi) 24B is the effective offset angle (psi) 24 for CVT 300.Assuming a positive effective offset angle (psi) 24 is more stable foroperation in a forward direction, CVT 300 may be configured foroperation in a forward direction with each of first offset angle (psi)24A and second offset angle (psi) 24B having any angle such thateffective offset angle (psi) 24 is positive, including combinations inwhich first offset angle (psi) 24A and second offset angle (psi) 24B areboth positive, first offset angle (psi) 24A is negative and secondoffset angle (psi) 24B is positive and larger in magnitude than firstoffset angle 24A, or first offset angle (psi) 24A is positive and secondoffset angle (psi) 24B is negative but first offset angle 24A is largerin magnitude than second offset angle 24B. Similarly assuming a negativeeffective offset angle (psi) 24 is more stable for operation in reversedirection 26, CVT 300 may be configured for operation in reversedirection 26 with each of first offset angle (psi) 24A and second offsetangle (psi) 24B having any angle such that effective offset angle (psi)24 is negative, including combinations in which first offset angle (psi)24A and second offset angle (psi) 24B are both negative, first offsetangle (psi) 24A is positive and second offset angle (psi) 24B isnegative and greater in magnitude than first offset angle (psi) 24A orfirst offset angle (psi) 24A is negative and second offset angle (psi)24B is positive but first offset angle (psi) 24A is greater in magnitudethan second offset angle (psi) 24B.

Embodiments disclosed herein may be controlled or configured such thatonly carrier half 310A is rotated, only carrier half 310B is rotated, orboth carrier 310A and 310B are rotated to angular position (beta) 29.

If the effective offset angle (psi) 24 is negative but needs to bepositive, a controller may determine which offset angle (psi) 24A or 24Bis positive and which offset angle (psi) is negative, and changing oneor both offset angles (psi) to be positive or changing one offset angle(psi) 24A or 24B to a positive angle such that the effective offsetangle (psi) 24 changes from negative to positive. Furthermore, inembodiments depicted in FIGS. 3A-3J, both links 321 are oriented in thesame direction (i.e., both trailing planets 108). However, embodimentsmay also be configured with one link 321 oriented in a forward directionand the other link 321 oriented in a reverse direction. In theseconfigurations, control of CVT 300 results in one link 321 being intension and the other link 321 being in compression. Control of CVT 300may involve only adjusting one link 321 of a pair of links.

FIGS. 3A-3J depict side and front partial views of CVT 300, illustratingcarrier 310 formed with carrier halves 310A, 310B rotatable aboutlongitudinal axis 15 to angular position (beta) 29 for imparting a skewangle (zeta) 27 on axles 103 to cause an adjustment of a tilt angle ofaxles 103 and therefore adjust to a target speed ratio of CVT 300 in,underdrive, overdrive configurations and 1:1 ratio, and in forward andreverse configurations.

As depicted in FIGS. 3A-3J, CVT 300 may be configured with links 321trailing planets 108. However, variations are possible, includingembodiments in which links 321 are leading planets and embodiments inwhich one link 321 is leading and the other link 321 is trailing.Embodiments in which one link 321 is leading and the other link 321 istrailing may avoid situations in which links 321 buckle or bind due totwo forces being applied in the same general direction.

CVT 300 comprises planets 108 located between and in contact withtraction rings 102, 104 and sun 110. Each planet 108 has a geometriccenter, with an x-axis, y-axis and z-axis intersecting at a geometriccenter of planet 108. The geometric centers collectively define pitchcircle 12 for the plurality of planets 108. Planets 108 are rotatablycoupled to axles 103. Tilting axles 103 to a non-zero tilt angle (gamma)causes contact points between planets 108 and traction rings 102, 104 tochange, thereby adjusting a speed ratio of CVT 300.

Axles 103 are rotatably coupled to planets 108 to allow planets 108 torotate about axes of rotation 106 defined by axles 103. Bearings 107allow rotation of planets 108 about axles 103. In some embodiments,bearings 107 allow planets 108 to rotate about axles 103 but constrainplanets 108 from movement along axles 103.

Links 321 are coupled to axles 103 on either side of planets 108. Asdepicted in FIGS. 3A-3J, links 321 are coupled to carrier arms 311A,311B of carrier halves 310A, 310B. Couplings 312 between links 321 andcarrier arms 311A, 311B allows for adjustment of offset angle (psi) 24A,24B of links 321 about axes of rotation 106 when carrier halves 310A,310B rotate. Couplings 312 between links 321 and carrier arms 311A, 311Bmay comprise pin 312 movable in slot 313 (as depicted) or some othercoupling. Links 321, couplings 312, or carrier arms 311A, 311B may beconfigured to allow axles 103 to be adjusted in any direction whilemaintaining planets 108 centered between traction rings 102, 104. Insome embodiments, couplings 312 comprise pins formed with arcuatesurfaces. In some embodiments, links 321 may be formed as resilientmembers capable of deflection. In some embodiments, carrier arms 311A,311B may be formed such that couplings 312 or links 321 are capable ofsome axial movement. Combinations of these embodiments and otherembodiments are possible.

In operation, links 321 may be rotated about axes of rotation 106 tooffset angle (psi) 24 and one or more of carrier halves 310A, 310B maybe rotated relative to each other to angular position (beta) 29 toimpart skew angle (zeta) 27.

FIGS. 3A-3C depict CVT 300 with links 321 coupled to carrier arms 311A,311B, wherein links 321 coupled to carrier arms 311A are configured atfirst offset angle (psi) 24A and links 321 coupled to carrier arms 311Bare configured at second offset angle (psi) 24B for forward rotation.Carrier halves 310A, 310B are rotated relative to each other to angularposition (beta) 29. As depicted in FIGS. 3A-3C, carriers 310A, 310B maybe rotated relative to each other such that an angular position (beta)29 is zero. Skew angle (zeta) 27 applied to axles 103 is zero, tiltangle (gamma) is zero, and power output on one side of CVT 300 equalspower input on the opposite side (minus any losses).

FIG. 3D depicts a partial cutaway view of one embodiment of CVT 300 withpins 312 radially positioned in slots 313 of carrier arms 311A, 311B.Links 321 coupled to carrier arms 311A may be configured at first offsetangle (psi) 24A and links 321 coupled to carrier arms 311B areconfigured at second offset angle 24B, whereby CVT 300 has an effectiveoffset angle (psi) 24 for forward rotation. Carrier halves 310A, 310Bmay be rotated relative to each other to angular position (beta) 29. Foreach non-zero angular position, axles 103 (and therefore axes ofrotation 106) are misaligned from a longitudinal axis of CVT 300,imparting a non-zero skew angle (zeta) 27. Rotation of each planet 108about a corresponding y-axis results in spin-induced (traction) forceson that planet 108. As these forces are exerted on planets 108, frictionand other forces in CVT 300 act to return CVT 300 to a balanced state,causing axles 103 to tilt to non-zero tilt angle (gamma) 28, resultingin CVT 300 operating in underdrive in forward rotation 25.

FIG. 3E depicts a partial cutaway view of one embodiment of CVT 300 withpins 312 radially positioned in slots 313 of carrier arms 311A, 311B.Links 321 coupled to carrier arms 311A are configured at first offsetangle (psi) 24A and links 321 coupled to carrier arms 311B areconfigured at second offset angle 24B, whereby CVT 300 has an effectiveoffset angle (psi) 24 for forward rotation. To adjust speed ratio,carrier halves 310A, 310B may be rotated relative to each other toangular position (beta) 29. For each non-zero angular position, axles103 (and therefore axes of rotation 106) are misaligned from alongitudinal axis of CVT 300, imparting a non-zero skew angle (zeta) 27.Rotation of each planet 108 about a corresponding y-axis results inspin-induced (traction) forces on that planet 108. As these forces areexerted on planets 108, friction and other forces in CVT 300 act toreturn CVT 300 to a balanced state, causing axles 103 to tilt tonon-zero tilt angle (gamma) 28, resulting in CVT 300 operating inoverdrive in forward rotation 25.

FIGS. 3F-3H depict partial side and front views of one embodiment of CVT300 configured for operating in reverse direction 26 at a 1:1 ratio.Comparing the radial positioning of pins 312 in slots 313 in carrierarms 311A in FIGS. 3A and 3F, pins 312 are positioned radially outwardof pitch circle 12 in FIG. 3A such that offset angle (psi) 24A ispositive, whereas pins 312 are positioned radially inward of pitchcircle 12 in FIG. 3F such that offset angle (psi) 24A is negative.Similarly, comparing the radial positioning of pins 312 in slots 313 incarrier arms 311B in FIGS. 3C and 3H, pins 312 are positioned radiallyoutward of pitch circle 12 in FIG. 3C such that offset angle (psi) 24Bis positive, whereas pins 312 are positioned radially inward of pitchcircle 12 in FIG. 3H such that offset angle (psi) 24B is negative.

As described above, CVT 300 depicted in FIGS. 3A-3J has links 321trailing planets 108, and effective offset angle (psi) 24 is positivefor operation in forward direction 25 and negative for operation inreverse direction 26. Furthermore, radially outward positioning pins 312for both links 321 may not be required for operation in forwarddirection 25, as long as effective offset angle (psi) 24 composed offirst offset angle (psi) 24A and second offset angle (psi) 24B ispositive. Similarly, radially inward positioning pins 312 for both links321 may not be required for operation in reverse direction 26, as longas effective offset angle (psi) 24 composed of first offset angle (psi)24A and second offset angle (psi) 24B is negative.

FIG. 3I depicts a partial cutaway view of one embodiment of CVT 300 withpins 312 radially positioned in slots 313 of carrier arms 311A, 311B.Links 321 coupled to carrier arms 311A are configured at first offsetangle (psi) 24A and links 321 coupled to carrier arms 311B areconfigured at second offset angle (psi) 24B, whereby CVT 300 has aneffective offset angle (psi) 24 for reverse rotation. To adjust speedratio, carrier halves 310A, 310B may be rotated relative to each otherto angular position (beta) 29. For each non-zero angular position, axles103 (and therefore axes of rotation 106) are misaligned from alongitudinal axis of CVT 300, imparting a non-zero skew angle (zeta) 27.Rotation of each planet 108 about a corresponding y-axis results inspin-induced (traction) forces on that planet 108. As these forces areexerted on planets 108, friction and other forces in CVT 300 act toreturn CVT 300 to a balanced state, causing axles 103 to tilt tonon-zero tilt angle (gamma) 28, resulting in CVT 300 operating inunderdrive in reverse rotation 26.

FIG. 3J depicts a partial cutaway view of one embodiment of CVT 300 withpins 312 radially positioned in slots 313 of carrier arms 311A, 311B.Links 321 coupled to carrier arms 311A are configured at first offsetangle (psi) 24A and links 321 coupled to carrier arms 311B areconfigured at second offset angle 24B, whereby CVT 300 has an effectiveoffset angle (psi) 24 for reverse rotation. To adjust speed ratio,carrier halves 310A, 310B may be rotated relative to each other toangular position (beta) 29. For each non-zero angular position, axles103 (and therefore axes of rotation 106) are misaligned from alongitudinal axis of CVT 300, imparting a non-zero skew angle (zeta) 27.Rotation of each planet 108 about a corresponding y-axis results inspin-induced (traction) forces on that planet 108. As these forces areexerted on planets 108, friction and other forces in CVT 300 act toreturn CVT 300 to a balanced state, causing axles 103 to tilt tonon-zero tilt angle (gamma) 28, resulting in CVT 300 operating inoverdrive in reverse rotation 26.

In some embodiments, carrier halves 310A, 310B or links 321 may becoupled to one or more actuators (not shown). An actuator may rotate oneor both carrier halves 310A, 310B to angular position (beta) 29 toimpart non-zero skew angle (zeta) 27 to cause axles 103 to tilt to tiltangle (gamma) 28 to adjust a speed ratio of CVT 300. An actuator maytranslate pins 312 radially inward or outward to adjust offset angle(psi) 24 to be positive or negative to configure CVT 300 for operationin forward direction 25 or reverse direction 26. An actuator may beactuated manually, such as by a person adjusting a lever or twisting agrip, or an actuator may be controlled electronically, such as by acontroller operating a set of instructions and communicatively coupledto an electronic servo, encoder, hydraulic pump, or other form ofactuation. An electronic controller may determine if CVT is to beoperated in forward direction 25 or reverse direction 26 and adjustoffset angle (psi) independently or concurrently with adjusting anangular position (beta), skew angle (zeta) 27 or tilt angle (gamma) 28.

A CVT capable of operation in forward direction and reverse direction isdescribed herein with respect to FIGS. 4A-4O in which axles 103 arecoupled to and controlled by a control system with trunnions 420, inwhich each planet 108 has a corresponding trunnion 420 that is rotatableabout a radial axis to induce a (non-zero) skew condition on planet 108and is further translatable radially to a positive offset angle (psi) 24or a negative offset angle (psi) 24, wherein CVT 400 is configured foroperation in forward rotation 25 or reverse rotation 26 depending onwhether offset angle (psi) 24 is positive or negative and whethertrunnion 420 leads or trails planet 108. FIGS. 4A-4O depict embodimentsin which trunnions 420 trail planets 108 for operation in forwarddirection 25 and lead planets 108 for operation in reverse direction 26.Variations are possible in which trunnions 420 lead planets 108 inforward direction 25 and trail planets 108 in reverse direction 26.

Rotating trunnion extension 213 rotates center link 422, advancing onelink 421 and receding a corresponding link 421. The advancement andrecession of links 421 may apply a non-zero skew condition on axles 103coupled to planets 108. A non-zero skew condition generates unbalancedforces, and the geometry and configuration of CVT 400 causes axles 103to tilt. Tilting axles 103 to a non-zero tilt angle (gamma) 28 causescontact points between planets 108 and traction rings 102, 104 tochange, adjusting a speed ratio of CVT 400.

CVT 400 comprises planets 108 located between and in contact withtraction rings 102, 104 and sun 110. Planets 108 are rotatably coupledto axles 103 such that planets 108 rotate about axes of rotation 106defined by axles 103. If present, bearings 107 allow rotation of planets108 about axles 103. In some embodiments, bearings 107 allow planets 108to rotate about axles 103 but constrain planets 108 from axial movementalong axles 103.

Planets 108 are fixed axially due to their position between tractionrings 102, 104 and traction sun 110, and are controllable due to theircoupling via axles 103, links 421, center link 422, trunnion extension213 and synchronizing ring 212.

Each trunnion 420 comprises trunnion extension 213 coupled to centerlink 422, which is coupled at each end to a pair of links 421. Trunnionextension 213 comprises a rigid member radially translatable in opening216 of synchronizing ring 212 and rotatable about axis 22. Center link422 is rigidly coupled to trunnion extension 213, whereby rotation oftrunnion extension 213 rotates center link 422. Each link 421 is coupledto one end of an axle 103 and center link 422, whereby rotation ofcenter link 422 advances a first link 421 and recedes a second link 421.

Trunnions 420 may be formed or configured for selected degrees offreedom between trunnion extensions 213 and planet axles 103. Forexample, in some embodiments, axles 103 may rotate about their y-axes 22but are constrained or fixed axially. In these embodiments, a couplingbetween links 421 and axles 103 may have only one degree of freedom. Inother embodiments, spherical joints or other couplings 415 allowmultiple degrees of freedom between links 421 and axles 103. In someembodiments, at least one link 421 may be formed as a resilient memberto provide at least one additional degree of freedom. In someembodiments, links 421 may be formed with directional resiliency orrigidity, whereby links 421 behave as rigid members relative to a firstdirection but behave as resilient members in a second direction. Forexample, when a torque is applied to links 421 relative to their z-axes,links 421 may behave as rigid members. However, when an axial force isapplied to links 421, links 421 may behave as resilient members in theaxial direction and allow some axial deflection, returning to theiroriginal configuration when the force is removed. An advantage todirectional resiliency in a control system for CVT 400 may be anincreased range of speed ratios or a smaller volume necessary for thecontrol system or CVT 400. For example, if trunnion extension 213,center link 422 and axles 103 are formed as rigid members, rotation oftrunnion extension 213 may be limited based on dimensions such as thewidth of trunnions 420, the width of center link 422, or the effectivelength of links 421, and rotation or translation of trunnions 420 mayexceed tolerances. However, links 421 having resilient properties,coupling 415 allowing multiple degrees of freedom, or other couplingsrelative to an axial direction may allow a control system for CVT 400 toflex or twist to remain within tolerances, which may extend the ratiorange of CVT 400.

Operationally, trunnion extension 213 is rotatable to skew angle (zeta)27 about radial line 22 to impart a non-zero skew condition on planetaxles 103. A non-zero skew condition, along with the geometry andconfiguration of CVT 400, generate unbalanced forces on planets 108. Thegeneration of forces due to the non-zero skew condition is a function ofthe rotation of trunnion 213, the length of center link 422, theeffective length of links 421, distance 424 between links 421, thelength of axles 103, the direction of rotation of CVT 400 or otherfactors. Unbalanced forces cause axles 103 to adjust toward tilt angle(gamma) 28 corresponding to a force-balanced state and a zero-skewcondition.

In addition to rotating trunnion 420 s about axes 22 to skew angle(zeta) 27, trunnion extensions 213 may be translated radially inward oroutward to rotate trunnions 420 about the z-axes for planets 108 tooffset angle (psi) 24, in which offset angle (psi) 24 may be defined asan angle between tangent line 21 and line 23 passing through theintersection of radial line 22 and center plane 14 which bisects centerlinks 422. A magnitude of offset angle (psi) 24 determines the stabilityand sensitivity for operation in forward direction 25 and reversedirection 26.

To enable control in forward direction 25, trunnion extension 213 may beradially translated to rotate trunnion 420 about z-axis of planets 108to offset angle (psi) 24. Rotation of trunnions 420 to a positive ornegative offset angle (psi) 24 results in a radial position of centerlinks 422 inward or outward of pitch circle 12. Radial positioning ofcenter links 422 outward of pitch circle 12 enables control of CVT 400in forward rotation 25. Radial positioning of center links 422 inward ofpitch circle 12 enables control of CVT 400 in reverse rotation 26.

FIGS. 4A-4C depict partial front and side views of one embodiment of CVT400 configured with center links 422 translated radially outwardrelative to pitch circle 12 for forward direction 25 and with trunnionextensions 213 rotated about axes 22 such that skew angle (zeta) 27 iszero, wherein forces are balanced and tilt angle (gamma) 28 is zero,whereby variator 400 is operating at a speed ratio of 1:1 (i.e., arotational speed of second traction ring 104 is substantially equal to arotational speed of first traction ring 102 minus any friction losses).

FIGS. 4D-4F depict partial front, side, and back views of one embodimentof CVT 400 configured with center links 422 translated radially outwardof pitch circle 12 for operation in a forward direction, and withtrunnion extensions 213 rotated about axes 22 to non-zero skew angle(zeta) 27, wherein unbalanced forces (e.g., spin-induced forces) causeaxles 103 to adjust to a non-zero tilt angle (gamma) 28, whereby CVT 400is operating in underdrive in forward direction 25.

FIGS. 4G-4H depict partial front and side views of one embodiment of CVT400 configured with center links 422 translated radially outward ofpitch circle 12 for operation in a forward direction 25, and withtrunnion extensions 213 rotated about axes 22 to non-zero skew angle(zeta) 27 to cause axles 103 to adjust to a non-zero tilt angle (gamma)28, whereby CVT 400 is operating in overdrive.

FIGS. 41-4K depict partial front and back views of one embodiment ofvariator 400 configured with center links 422 translated radially inwardof pitch circle 12 for operation in a reverse direction 26, and withtrunnion extensions 213 rotated about axes 22 to non-zero skew angle(zeta) 27 to cause an adjustment of axles 103 to a non-zero tilt angle(gamma) 28 such that CVT 400 is operating at a 1:1 ratio.

FIGS. 4L-4M depict partial front and back views of one embodiment of CVT400 configured with center links 422 translated radially inward of pitchcircle 12 for operation in a reverse direction 26, and with trunnionextensions 213 rotated about axes 22 to non-zero skew angle (zeta) 27 tocause an adjustment of axles 103 to a non-zero tilt angle (gamma) 28whereby CVT 400 is operating in underdrive.

FIGS. 4N-4O depict partial front and back views of one embodiment of CVT400 configured with center links 422 translated radially inward of pitchcircle 12 for stable operation in a reverse direction 26, and withtrunnion extensions 213 rotated about axes 22 to non-zero skew angle(zeta) 27 to cause an adjustment of axles 103 to a non-zero tilt angle(gamma) 28 whereby CVT 400 is operating in overdrive.

Embodiments disclosed in FIGS. 4A-4O may be controlled manually, such asby a person rotating a hand grip, lever, or other mechanical actuator.Embodiments disclosed in FIGS. 4A-4O may also be controlledelectronically, such as by a controller communicatively coupled to oneor more actuators (not shown), whereby the controller receives inputregarding a target operating condition of CVT 400 and adjusts one ormore of skew angle (zeta) 27 and offset angle (psi) 24 to adjust a tiltangle (gamma) 28 of CVT 400 for operation in forward direction 25 orreverse direction 26. The target operating condition may be a targetspeed ratio, target ratio, output speed or input speed. The controllermay determine a direction of operation (e.g., forward direction 25 orreverse direction 26) and adjust offset angle (psi) 24 accordingly. Asthe magnitude of offset angle (psi) 24 increases, the stability of CVT400 increases. As the magnitude of offset angle (psi) 24 nears zero, thesensitivity of CVT 400 increases.

As mentioned above, CVTs described herein may be operated in forward andreverse directions, such as by rotating trunnions 220, 320 or 420 aboutthe z-axes of planets 108 to an offset angle (psi) 24 associated withforward direction 25 or reverse direction 26. In addition to enablingcontrol in forward and reverse, embodiments disclosed herein may beconfigured for more stability or more sensitivity.

Referring to FIGS. 2A-2J, the more radially inward or outward coupling215 is moved (i.e., a magnitude of an offset angle (psi) is closer to amaximum possible magnitude for psi), the more stable CVT 200 mayoperate, whereas radial translation of coupling 215 toward a neutraloffset angle (psi) 24 (i.e., a magnitude of an offset angle (psi) iscloser to zero), the faster CVT 200 may be adjusted.

-   -   In some embodiments, a controller may be configured to determine        a target offset angle (psi) based on a target stability or        sensitivity. For example, a controller may control CVT by        configuring trunnion 220 to a maximum offset angle (psi) for        stability and reducing the frequency at which zeta angle is        changed. This example may work well in scenarios in which        undesirable or unexpected rollback or operation in reverse        direction 26 is unlikely to occur. An advantage to this control        scheme may be reduced power consumption by an actuator used to        adjust a speed ratio of CVT 200.    -   In some embodiments, operating CVT 200 with the magnitude of        offset angles (psi) 24 always close to zero may be useful in        scenarios in which an unexpected or unfavorable rollback or        operation in reverse direction 26 may occur. An advantage to        this control scheme may be the ability to rapidly switch between        operation in forward direction and reverse direction. A        controller may be configured with at least two control schemes,        wherein one control scheme configures CVT 200 into a stable        configuration with higher magnitude offset angles (psi), and a        sensitive configuration with the magnitude of offset angles        (psi) closer to zero.

Referring to FIGS. 3A-3J, the larger offset angle (psi) 24 to whichlinks 321 are rotated (i.e., a magnitude of an offset angle (psi) iscloser to a maximum possible magnitude for psi), the more stable CVT 300may operate, whereas the smaller offset angle (psi) 24 to which links321 are rotated (i.e., a magnitude of an offset angle (psi) is closer tozero), the faster CVT 300 may be adjusted for a given skew angle (zeta)27. A controller may be configured to determine offset angle (psi) basedon a target stability or sensitivity.

-   -   In some embodiments, a controller may control CVT by configuring        trunnion 320 to a maximum offset angle (psi) 24 for stability        and reducing the frequency at which skew angle (zeta) 27 is        changed. This example may work well in scenarios in which        unfavorable or unexpected rollback or operation in reverse        direction 26 is unlikely to occur. An advantage to this control        scheme may be reduced power consumption by an actuator used to        adjust a speed ratio of CVT 300.    -   In some embodiments, operating CVT 300 with the magnitude of        offset angles (psi) 24 always close to zero may be useful in        scenarios in which an unexpected or unfavorable rollback or        operation in reverse direction 26 may occur. An advantage to        this control scheme may be the ability to rapidly switch between        operation in forward direction and reverse direction.

A controller may be configured with at least two control schemes,wherein one control scheme configures CVT 300 into a stableconfiguration with higher magnitude offset angles (psi), and a sensitiveconfiguration with the magnitude of offset angles (psi) closer to zero.In some embodiments, an offset angle (psi) greater than 10 degrees mayprovide a stable configuration. In some embodiments, an offset angle(psi) greater than 12 degrees may provide a stable configuration. Insome embodiments, an offset angle (psi) greater than 15 degrees mayprovide a stable configuration. In some embodiments, an offset angle(psi) less than 10 degrees may provide a sensitive configuration. Insome embodiments, an offset angle (psi) less than 7 degrees may providea sensitive configuration. In some embodiments, an offset angle (psi)less than 5 degrees may provide a sensitive configuration.

A controller may be coupled to a user interface and a plurality ofsensors. User inputs may be received by the controller from the userinterface. A user input may include a target speed ratio, a direction ofrotation, a control scheme, or some combination. In some embodiments, auser input may be interpreted by the controller. For example, a user mayselect “Economy” and “Forward” and the controller may interpret the userinput to configure a CVT with a positive, larger magnitude offset angle(psi) 24 for stable control in forward rotation, or a user may select“Low” and “Forward” and the controller may recognize that operation inthis combination may be an indicator that rollback is likely andconfigure a CVT with a positive, lower magnitude offset angle (psi).

Referring to FIGS. 4A-4O, the more radially inward or outward thatcenter links 422 are positioned (i.e., the larger offset angle (psi) 24to which links 421 are rotated such that a magnitude of an offset angle(psi) is closer to a maximum possible magnitude), the more stable CVT400 may operate, whereas the closer to pitch circle 12 that center links422 are positioned, the faster CVT 400 may be adjusted for a given skewangle (zeta) 27.

-   -   In some embodiments, a controller may be configured to determine        offset angle (psi) 24 based on a target stability or        sensitivity. For example, a controller may control CVT 400 by        positioning center links 422 to configure CVT 400 with a maximum        offset angle (psi) 24 for stability and reducing the frequency        at which skew angle (zeta) 27 is changed. This example may work        well in scenarios in which undesirable or unexpected rollback or        operation in reverse direction 26 is unlikely to occur. An        advantage to this control scheme may be reduced power        consumption by an actuator used to adjust a speed ratio of CVT        400.    -   In some embodiments, operating CVT 400 with the magnitude of        offset angle (psi) 24 always close to zero may be useful in        scenarios in which an unexpected or unfavorable rollback or        operation in reverse direction 26 may occur. An advantage to        this control scheme may be the ability to rapidly switch between        operation in forward direction and reverse direction. A        controller may be configured with at least two control schemes,        wherein one control scheme configures CVT 400 into a stable        configuration with higher magnitude offset angles (psi), and a        sensitive configuration with the magnitude of offset angles        (psi) closer to zero.

As described herein, planets 108 may be in contact with traction rings102, 104 and sun 110. Contact may be direct or may include embodimentsin which a traction fluid between contact points allows CVT 200, 300 or400 to behave as if there is direct contact between components.

Operation in reverse direction 26, as described herein, may refer topowered and unpowered events in which a CVT is rotated in a directionopposite a design direction.

Embodiments disclosed herein may include a controller executing a set ofinstructions for a control process. As used herein, the term “shutdown”refers to a process or sequence in which power is removed from allelectronic components. Shutdown may therefore include removing powerfrom an electronic control unit (ECU), user displays, and the like, andmay also include removing power from actuators, hydraulic andlubrication pumps, fans and other auxiliary and accessory devices.

A control process may include a controller tracking speed ratio, whichmay involve the controller tracking tilt angle (gamma) 28. Referring toembodiments of CVT 200, 300 or 400, in some embodiments, a controllermay track speed ratio based on skew angle (zeta) 27. In someembodiments, a controller may track speed ratio relative to distance Dthat ring 212 is translated axially in CVT 200. In some embodiments, acontroller corresponding to CVT 300 may track speed ratio based on arelative angular position (beta) of carrier halves 310A, 310B. In someembodiments, a controller corresponding to CVT 400 may track speed ratiobased on skew angle (zeta) 27 of trunnion extensions 213. Variations inCVT geometry and components will allow for other ways to track speedratio directly or indirectly. In some embodiments, tracking speed ratiousing direct or indirect measurements may be performed once reversespeed is detected, and a controller may remain on an upshift (forwardadjustment) side of the tracked speed ratio.

Examples of operation in reverse direction include the followingscenarios:

In this scenario, vehicle speed is zero prior to shutdown, the primemover is turned off, the controller is powered down, a range box (ifpart of the drivetrain) is in gear (forward or reverse), and the vehiclerolls in a direction opposite of the gear range selection. An example ofthis scenario occurs when a vehicle is stopped in a gear range on flatground and powered off, but the vehicle is pushed or pulled in anopposite direction of the range. The controller is powered down, sodownshift cannot be tracked as the vehicle rolls back and the CVT maylock if the planet axles translate into certain configurations. Acontrol process may include the controller sensing when the vehiclestops (or is about to stop). The controller may impart a skew angle(zeta) to cause a slight upshift to the speed ratio before thecontroller is powered down, or the controller may, upon receiving asignal to power down, impart a skew angle (zeta) to cause a slightupshift to the speed ratio. In some embodiments, when the controlleridentifies a condition or set of conditions that may possibly result ina rollback situation, the controller may execute a set of instructionsthat result in a control system operating with a magnitude of an offsetangle (psi) being closer to zero and with higher frequency datasampling. The magnitude of the offset angle (psi) may be greater than 3degrees but less than 10 degrees, less than 5 degrees, or some otherangle or range of angles that allows control of the CVT and is able toswitch directions if needed.

In this scenario, vehicle speed is zero prior to shutdown, the primemover is turned off, the controller is powered down, a range box (ifpart of the drivetrain) is in gear (forward or reverse), and the vehiclerolls in opposite direction of range selection. An example is if thevehicle stalls when traversing a hill and subsequently rolls backward.This scenario might be more common than the standard shutdown sincethere might not be enough time to adjust the transmission to underdrive.A challenge is that a tilt angle of the planet axles might not betracked as the vehicle rolls back and the CVT may lock if the planetaxles translate into certain configurations. A control process mayinclude the controller sensing when the vehicle stalls (or is about tostall) and imparting a skew angle (zeta) to cause a slight upshift tothe speed ratio before the controller powers down or changing an offsetangle (psi) to, or the controller, upon receiving a signal indicatingthe engine has stalled and the controller is about to power down,imparting a skew angle (zeta) to cause a slight upshift to the speedratio. In some embodiments, when the controller identifies a conditionor set of conditions that are likely to result in a rollback situation,the controller may execute a set of instructions that result in acontrol system operating with a magnitude of an offset angle (psi) beingcloser to zero and with higher frequency data sampling. The magnitude ofthe offset angle (psi) may be greater than 3 degrees but less than 7degrees, less than 5 degrees, or some other angle or range of anglesthat allows control of the CVT and is able to switch directions ifneeded.

In this scenario, the vehicle speed may be zero, with the prime moverspeed below a clutch engagement point, such that even with a range boxin gear (either forward or reverse), the vehicle rolls in the oppositedirection of range selection. An example of this scenario is when adriver stops on a slope and releases the brake before either applyingsufficient throttle to go forward or engaging a parking brake to preventthe vehicle from rolling backward. There may be different controlprocesses, depending on the circumstances. The controller performs acontrol process to adjust a CVT to a slight upshift (forward adjustment)when the vehicle stops. If the vehicle is equipped with accelerometersor other sensors that allow the vehicle to detect slopes, a controlprocess performs a slight upshift when a vehicle comes to a stop and acontroller has determined that the vehicle is on a slope. Once reversespeed is detected, a controller may ensure a CVT remains on an upshiftside of a target speed ratio. In some embodiments, when the controlleridentifies a condition or set of conditions that indicate a rollbacksituation, the controller may execute a set of instructions that resultin a control system changing a sign of the offset angle (psi), operatingwith a magnitude of an offset angle (psi) being closer to zero, and withhigher frequency data sampling. The magnitude of the offset angle (psi)may be greater than 3 degrees but less than 10 degrees, less than 5degrees, or some other angle or range of angles that allows control ofthe CVT and is able to switch directions if needed.

In this scenario, the vehicle speed is zero, the prime mover speed isabove a clutch engagement point, but the clutch is slipping and nottransmitting torque to the drivetrain, the range box is in gear (forwardor reverse) but the vehicle rolls in an opposite direction of the rangeselection. This may be due to the slope, towing, pushing, or some otherexternal factor. This scenario may occur when a vehicle is on a steepergrade and the driver remains on the throttle but not enough to overcomethe grade. In some embodiments, the controller executes instructions ina control process to adjust a CVT to a slight upshift (perform a forwardadjustment) when the vehicle speed reaches zero. In some embodiments,tracking speed ratio using direct or indirect measurements may beperformed once reverse speed is detected, and a controller may remain onan upshift (forward adjustment) side of the tracked speed ratio. Achallenge with this scenario or control process is that timing of anupshift may be critical, as the timing between when wheel speed is zeroand rollback begins may be very short. In some embodiments, when thecontroller identifies a condition or set of conditions that indicate apowered rollback situation, the controller may execute a set ofinstructions that result in a control system changing an offset angle(psi) of the CVT, operating with a magnitude of an offset angle (psi)closer to zero, changing the skew angle (zeta) to keep the CVT operatingin a target range (overdrive or underdrive), and increasing the rate offrequency data sampling. Using CVT 200 depicted in FIGS. 2A-2J as anexample, if CVT 200 is operating in overdrive in a forward direction(such as depicted in FIG. 2E) and encounters a powered rollbacksituation, a controller may execute a set of instructions to restrictthe magnitude of the offset angle (psi) to be greater than 3 degrees butless than 10 degrees and ring 212 may be axially translated from aposition near first traction ring 102 to a position near second tractionring 104 to keep CVT 200 in overdrive (as depicted in FIG. 2I), or anaxial position of ring 212 may be maintained to switch operation of CVT200 from overdrive to underdrive (as depicted in FIG. 2J). The CVT maybe operated at some other angle or range of angles that allows controlof the CVT and is able to switch directions if needed.

In this scenario, the vehicle speed is non-zero and the range box is ingear. There may be a fast transition from throttle to brake, the primemover speed may remain high and the clutch may be engaged. Furthermore,the brakes may be applied hard, inducing wheel lock. This scenario mayoccur, for example, when there is an emergency stop on a slope, and thedriver then releases the brake before reapplying the throttle orengaging a parking brake, or may occur if there is an emergency stop onflat ground but is then pushed or towed in an opposite direction. Insome embodiments, a controller executes a set of instructions in acontrol process to downshift the CVT rapidly to avoid stalling theengine, such that power is constantly applied to the CVT controller. Acontrol process may include the controller slightly upshifting (forwardadjustment) a speed ratio of the CVT as the wheel speed nears zero. Insome embodiments, once reverse speed is detected, the controller mayexecute a set of instructions to keep a CVT on an upshift (forwardadjustment) of a target speed ratio. A challenge may be to thedifficulty in smoothly tracking a relationship between wheel and enginespeed at high wheel deceleration rates. A challenge is that rollback maybe more likely when the throttle is reengaged if the CVT is not fullydownshifted.

In this scenario, the vehicle speed is non-zero and the range box is ingear. The wheels lose traction and spin, so the transmission upshifts(adjusts forward). The vehicle may slow to a stop and the driverreleases the throttle, so the prime mover is at idle and the clutch isopen. The vehicle may roll in the opposite direction of range selection.This scenario may occur, for example, if the vehicle is climbing a hillof loose material, there is loss of traction, and the driver releasesthe throttle. The controller performs a control process to increase aspeed ratio of the CVT when the wheels break loose. The controller mayalso perform a control process to slightly increase the speed ratio ofthe CVT when the wheel speed reaches zero. A control process may includetracking a ratio (or track a corresponding parameter such as tilt angle(gamma) 28) with beta angle 29, remaining in an upshift side of presentspeed ratio. A challenge with existing CVTs includes the difficulty insmoothly tracking a relationship between wheel speed and engine speed athigh wheel acceleration rates. Also, in some prior approaches, tiltangle (gamma) 28 must be tracked through a full ratio sweep. Embodimentsdisclosed herein may mitigate this challenge by allowing a controller toexecute a control process that is able to independently adjust speedratio and offset angle, such that the CVT may be adjusted quickly for awide range of conditions. If the transmission is already at the highestspeed ratio, further increases are not possible and a controller mayexecute a set of instructions to maintain a maximum skew angle (zeta)and the rate of data sampling may decrease.

In this scenario, the vehicle speed is non-zero and the range box is ingear. The wheels lose traction and spin, so the speed ratio of a CVTincreases. The vehicle may slow but then regain traction, so the driverremains on the throttle and the input clutch experiences slipping. Thevehicle may roll in the opposite direction of range selection. Thisscenario may occur, for example, if the vehicle is climbing a loosehill, there is loss of traction, but the driver remains on the throttleand traction is regained. A control process may be a rapid increase ofspeed ratio when the wheels break loose. A control process for a CVT mayinclude increasing a skew angle (zeta) to cause a slight upshift whenthe wheel speed reaches zero. In some embodiments, a controller maytrack a speed ratio and adjust the skew angle (zeta) to remain inupshift side of a target speed ratio. Tracking a relationship betweenwheel speed and engine speed at high wheel acceleration rates may bedifficult, rollback may be more likely due to an upshift prior tostalling, and tilt angle (gamma) must be tracked through a full ratiosweep. Embodiments disclosed herein may mitigate this challenge byallowing a controller to execute a control process that is able toindependently adjust speed ratio and offset angle, such that the CVT maybe adjusted quickly for a wide range of conditions. If the transmissionis already fully upshifted to full overdrive, further upshifting toenable rollback is not possible. Embodiments disclosed herein mayaddress operation in reverse direction—including rollback—ofcontinuously variable transmissions. Embodiments described herein may beparticularly useful for controlling CVTs by imparting a skew angle(zeta) on a plurality of planets to control a transmission ratio.

A drivetrain may include a prime mover, a CVT, and a control system. Aprime mover generates power. Power may be delivered at a constant speedlevel or at varying (including modulating) speed levels, which dependon, among other things, user inputs or output power. A planetary gearset allows a drive train having a CVT to operate in various modes. Byselectively locking or unlocking one or more of a sun gear, a set ofplanet gears, or a ring gear, the drive train can operate in variousmodes including, but not limited to, low mode, high mode, forward mode,or reverse mode. For example, power may be input through the sun gear,and by locking a ring gear, power exits the set of planet gears, but ina reverse direction. A control system receives signals indicatingoperating conditions for one or more of the prime mover, clutches, aplanetary gear set, a CVT and a differential, and sends control signalsto one or more of the prime mover, the clutches, the planetary gear setand the CVT. The control signals ensure a target performance of thedrivetrain. In some embodiments, signals indicating operating conditionsof a prime mover are not received. However, in other embodiments,signals indicating operating conditions of a prime mover are received,allowing embodiments to take advantage of the capabilities of a CVT andoptimize performance of the prime mover as well as the performance of anauxiliary device or accessory on a vehicle. A control system for a CVTemploying a plurality of tiltable balls may receive signals indicating atarget direction of rotation and an actual direction of rotation.Signals indicating a target direction of rotation may include userinputs, signals from an accelerometer, throttle or other vehicle sensor,signals from a global positioning system (GPS) or other external source,including combinations thereof. Signals indicating an actual directionof rotation may include signals from accelerometers or similar systemsindicating relative movement, signals from pickups or other sensorsdirectly sensing (or measuring) parameters of internal components, orenvironmental sensors capable of determining motion of a vehicle basedon changes in the surroundings. In some embodiments, the control systemis configured to determine an unintended change in the direction ofrotation based on an indication of brake pressure or an increase inbrake pressure and/or reduced vehicle speed or a vehicle speed below apredetermined threshold. The threshold may be constant or may varyaccording to several factors, including but not limited to, a load, apitch angle, a roll angle, wheel speed, vehicle speed, hydraulicpressure, brake pressure, or some other factor or combination offactors. For example, if the wheel speed is low relative to vehiclespeed, embodiments may determine the vehicle is slipping, or high brakepressure in combination with any non-zero vehicle speed may determinethe vehicle operator is trying to stop the vehicle. Hydraulic pressuremay indicate a load. A pitch angle and a roll angle (and thecombination) are examples of factors that might help determineconditions in which rollback is more likely to occur. A control systemmay be configured to determine an unintended change in the direction ofrotation based on a comparison of engine speed and vehicle speed,including acceleration (a rate of change of vehicle speed). For example,a controller may receive signals from an engine speed sensor indicatingthe engine is operating at an increased speed and a vehicle speed sensorindicating the vehicle speed is decreasing. This comparison may indicatethe wheels are slipping. The controller may then perform any processesnecessary to counteract the effects of operation in reverse direction ofa CVT. For example, in some embodiments, a control system is configuredto impart an additional skew condition to each planet. In someembodiments, a control system is configured to send an indication toincrease throttle of the prime mover. Other signals and indicators maybe used to determine when operation in reverse direction is possible orlikely. For example, in some embodiments, a control system is configuredto determine if a clutch is slipping, if the vehicle is on a slopelikely to result in the vehicle stalling.

In operation, a prime mover generates power having an associated torqueand speed. Power may be transmitted directly to the CVT, such as by adirect coupling the prime mover to the CVT, or indirectly through anelement such as a shaft, sprocket, chain, belt, pulley or planetary gearset to the CVT. Power from the CVT may be transmitted either directly orindirectly to a downstream gear set. A gear set may be configured for anoutput torque or speed. For example, power may enter a planetary gearset via an outer ring but may exit the planetary gear set via a sungear. Alternatively, a planetary gear set may be configured to allowpower to enter via a carrier, a sun gear, a planet gear or somecombination. Similarly, a planetary gear set may be configured to allowpower to exit the planetary gear set via the outer ring, the planetgears, the carrier, the sun gear, or some combination. A control systemreceives signals related to the operation of the prime mover or CVT andoptimizes one or more of the prime mover operation or the CVT operationbased on a target output parameter or operating condition. For example,a result may be based on efficiency or acceleration (power transfer).

Embodiments disclosed herein may provide additional advantages. Forexample, embodiments disclosed with respect to CVT 200 and 400 are freefrom side components, which may allow for better circulation oflubrication using unpowered techniques (e.g., “splash lubrication”),whereas embodiments disclosed with respect to CVT 300 may includelubrication channels, ports, or other fluid delivery systems in carriers310A, 310B for powered or directed lubrication.

Embodiments disclosed herein are exemplary. Other modifications may bepossible that are still within the scope of the disclosure. For example,FIGS. 2A-2J depict embodiments in which axles 103 are axially fixed toplanets 108 and planets 108 are axially fixed by other componentsincluding first traction ring 102, second traction ring 104, and sun 110such that tilting planets 108 is accomplished by an axial translation oftrunnion extensions 215.

A variation of an embodiment of FIGS. 2A-2J is also described in whichtrunnion extensions 215 are axially fixed, and axles 103 are axiallytranslatable relative to planets 108 to tilt planets 108. A person ofskill in the art will appreciate, after reading this disclosure, that avariation may be possible in which a third point is located along theline AB between point A (the intersection of axis of rotation 106 and amidplane of axles 103) and point B (a geometric center of couplings 215)in which axles 103 may be translated axially in a first direction andcouplings 215 may be translated axially in an opposite direction tocause planets 108 to tilt, wherein the distance that point A and point Bare translated depend on the location of the third point on line AB.

As another example of variations possible within the scope of thedisclosed technology, FIGS. 3A-3J depict one embodiment in which links321 are coupled between axles 103 and carrier arms 311 via pins or othercouplings 312. Rotation of carriers 310A, 310B to adjust carrier arms311 may require multiple degrees of freedom. Pins 312 are depicted inslots 313. Pins may be spherical or have some other arcuate surface toprovide multiple degrees of freedom. Links 321 may also provide one ormore degrees of freedom. Other configurations and materials may provideother degrees of freedom, may improve degrees of freedom, may providedirectional degrees of freedom. In FIGS. 3A-3J, carrier arms 311A, 311Bare depicted generally as radial spokes. However, in some embodiments,carrier arms 311A, 311B may be curved (in an axial, radial or angulardirection), angled, or otherwise configured to provide degrees offreedom.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, article, orapparatus.

Further, unless expressly stated to the contrary, “or” refers to aninclusive or and not to an exclusive or. That is, the term “or” as usedherein is generally intended to mean “and/or” unless otherwiseindicated. For example, a condition A or B is satisfied by any one ofthe following: A is true (or present) and B is false (or not present), Ais false (or not present) and B is true (or present), and both A and Bare true (or present).

As used herein, a term preceded by “a” or “an” (and “the” whenantecedent basis is “a” or “an”) includes both singular and plural ofsuch term unless the context clearly dictates otherwise. Also, as usedherein, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise.

Additionally, any examples or illustrations given herein are not to beregarded in any way as restrictions on, limits to, or expressdefinitions of, any term or terms with which they are utilized. Instead,these examples or illustrations are to be regarded as being describedwith respect to one particular embodiment and as illustrative only.Those of ordinary skill in the art will appreciate that any term orterms with which these examples or illustrations are utilized willencompass other embodiments that may or may not be given therewith orelsewhere in the specification and all such embodiments are intended tobe included within the scope of that term or those terms.

Reference throughout this specification to “one embodiment,” “anembodiment,” or “a specific embodiment” or similar terminology meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodimentand may not necessarily be present in all embodiments. Thus, respectiveappearances of the phrases “in one embodiment,” or “in an embodiment,”or similar terminology in various places throughout this specificationare not necessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics of any particularembodiment may be combined in any suitable manner with one or more otherembodiments. It is to be understood that other variations andmodifications of the embodiments described and illustrated herein arepossible in light of the teachings herein and are to be considered aspart of the spirit and scope of the disclosed technology.

Although the disclosed technology has been described with respect tospecific embodiments thereof, these embodiments are merely illustrative,and not restrictive of the disclosed technology. The description hereinof illustrated embodiments of the disclosed technology is not intendedto be exhaustive or to limit the disclosed technology to the preciseforms disclosed herein (and in particular, the inclusion of anyparticular embodiment, feature or function is not intended to limit thescope of the disclosed technology to such embodiment, feature orfunction). Rather, the description is intended to describe illustrativeembodiments, features and functions in order to provide a person ofordinary skill in the art context to understand the disclosed technologywithout limiting the disclosed technology to any particularly describedembodiment, feature or function. While specific embodiments of, andexamples for, the disclosed technology are described herein forillustrative purposes only, various equivalent modifications arepossible within the spirit and scope of the disclosed technology, asthose skilled in the relevant art will recognize and appreciate. Asindicated, these modifications may be made to the disclosed technologyin light of the foregoing description of illustrated embodiments of thedisclosed technology and are to be included within the spirit and scopeof the disclosed technology. Thus, while the disclosed technology hasbeen described herein with reference to particular embodiments thereof,a latitude of modification, various changes and substitutions areintended in the foregoing disclosures, and it will be appreciated thatin some instances some features of embodiments of the disclosedtechnology will be employed without a corresponding use of otherfeatures without departing from the scope and spirit of the disclosedtechnology as set forth. Therefore, many modifications may be made toadapt a particular situation or material to the essential scope andspirit of the disclosed technology.

In the description herein, numerous specific details are provided, suchas examples of components and/or methods, to provide a thoroughunderstanding of embodiments of the disclosed technology. One skilled inthe relevant art will recognize, however, that an embodiment may be ableto be practiced without one or more of the specific details, or withother apparatus, systems, assemblies, methods, components, materials,parts, and/or the like. In other instances, well-known structures,components, systems, materials, or operations are not specifically shownor described in detail to avoid obscuring aspects of embodiments of thedisclosed technology. While the disclosed technology may be illustratedby using a particular embodiment, this is not and does not limit thedisclosed technology to any particular embodiment and a person ofordinary skill in the art will recognize that additional embodiments arereadily understandable and are a part of this disclosed technology.

Although the steps, operations, or computations may be presented in aspecific order, this order may be changed in different embodiments. Insome embodiments, to the extent multiple steps are shown as sequentialin this specification, some combination of such steps in alternativeembodiments may be performed at the same time. The sequence ofoperations described herein can be interrupted, suspended, or otherwisecontrolled by another process.

It will also be appreciated that one or more of the elements depicted inthe drawings/figures can also be implemented in a more separated orintegrated manner, or even removed or rendered as inoperable in certaincases, as is useful in accordance with a particular application.Additionally, any signal arrows in the drawings/figures should beconsidered only as exemplary, and not limiting, unless otherwisespecifically noted.

What is claimed is:
 1. A continuously variable transmission (CVT) havinga central axis, the CVT comprising a plurality of planet assembliesconfigured for transferring power between first and second tractionrings, each planet assembly fixed in its radial position by the firstand second traction rings and a sun, each of the plurality of planetassemblies comprising a spherical planet coupled to a planet axle, theplanet axle defining an axis of rotation for its respective planet, eachplanet axle capable of tilting in a first skew plane, a skew angledefined as a first angle in a first direction between the central axisand the planet axle, and in a second tilting plane defining a tilt angleas a second angle in a second direction between the central axis and theplanet axle, wherein the tilt angle defines a transmission ratio of theCVT, the CVT further comprising: a first carrier half coaxial with andpartially rotatable about the central axis, the first carrier halfcoupled by a plurality of links to a first end of each of the planetaxles; a second carrier half coaxial with and rotatable about thecentral axis, the second carrier half coupled by a plurality of links toa second end of each of the planet axles, wherein the first carrier halfand second carrier half are rotatable with respect to each other todefine an angular position, wherein the first carrier half and thesecond carrier half are limited in relative rotation to a maximumangular position with respect to each other; wherein relative rotationof the first and second carrier halves defines a non-zero angularposition that imparts a non-zero skew angle, and wherein the non-zeroskew angle imparts an adjustment to the tilt angle, resulting in achange in the transmission ratio of the CVT; and a plurality ofcouplings that couple the plurality of links to the first and secondcarrier halves, wherein the plurality of couplings are adapted to allowthe plurality of links to rotate out of plane with the first and secondcarrier halves to facilitate the tilting of the planet axles.
 2. The CVTof claim 1, wherein the plurality of couplings are ball joints.
 3. TheCVT of claim 1, wherein the plurality of links are flexible.
 4. The CVTof claim 1, further comprising: a pitch circle coaxial about the centralaxis and having a radius equal to a plurality of centers of the planetassemblies; and a plurality of connections that connect the plurality oflinks to the plurality of planet axles, an effective offset angledefined by the tangent of the pitch circle at a respective one of theplurality of connections and a line between an associated one of theplurality of connections and an associated one of the plurality ofcouplings, wherein the effective offset angle is positive when theplurality of links are located radially outside of the pitch circle, apositive offset angle associated with a forward direction of rotation,and wherein the effective offset angle is negative when the plurality oflinks are located radially inside of the pitch circle, a negative offsetangle associated with a reverse direction of rotation.
 5. The CVT ofclaim 4, further comprising an actuator adapted to adjust the radialposition of the plurality of couplings in order to adjust the effectiveoffset angle.
 6. The CVT of claim 5, wherein the actuator is adapted toadjust the radial position of the plurality of couplings to a positiveeffective offset angle when the CVT is rotating in the forwarddirection, and wherein the actuator is adapted to adjust the radialposition of the plurality of couplings to a negative offset angle whenthe CVT is rotating in the reverse direction.